So this is what my code looks like. I am a mathematica total beginner. I just want to use it to some calculations and the reason mathematica is so interesting or attractive to me as an engineering student is that it allows you to write maths symbolically as you would see in a textbook. My mind cannot comprehend mathematics if it is written in code form. So this is my code so far:

        Power Screws
    
    
    raise = Subscript[M, 
      t] == (W*Subscript[d, m])/
        2*((f*\[Pi]*Subscript[d, m] + 
          L*Cos[Subscript[\[Alpha], n]])/(\[Pi]*Subscript[d, m]*
           Cos[Subscript[\[Alpha], n]] - f*L)) + (
       W*Subscript[f, c]*Subscript[d, c])/2
    lower = Subscript[M, 
      t] == (W*Subscript[d, m])/
        2*((f*\[Pi]*Subscript[d, m] - 
          L*Cos[Subscript[\[Alpha], n]])/(\[Pi]*Subscript[d, m]*
           Cos[Subscript[\[Alpha], n]] + f*L)) + (
       W*Subscript[f, c]*Subscript[d, c])/2
    
    stress = \[Sigma] == (-4 p W)/(\[Pi] h*(Subscript[d, 0]^2 - Subscript[d, r]^2))
    eff = \[Eta] == (W L)/(2 \[Pi] Subscript[M, t])
    power = w == (2 \[Pi] (6/n*60) Subscript[M, t])/60
    
    
    
    
    (*Question 2*)raise /. {Subscript[M, t](*Changes*)-> (101.5) (125/1000), 
      Subscript[d, m] -> 18.75/1000, f -> 0.15, Subscript[f, c] -> 0.15, 
      L -> 2.5/1000, Subscript[\[Alpha], n] -> 14.5 Degree, 
      Subscript[d, c] -> 12/1000} 
    
    (*Question 3*)eff /. {W(*Changes*)-> 4592.508217189424, L -> 2.5/1000, 
      Subscript[M, t] -> 6.62183}
    
    (*Question 4*)stress /. {W(*Changes*)-> 4592.51, \[Sigma](*Changes*)-> 
       12.1*10^6, Subscript[d, 0] -> 20/1000, Subscript[d, r] -> 17.5/1000, 
      p -> 2.5/1000}
    
    (*Question 6*)raise /. {Subscript[d, m] -> 22.5/1000, f -> 0.08, 
      Subscript[f, c] -> 0.05, L -> 5/1000, Subscript[\[Alpha], n] -> 0 Degree, 
      Subscript[d, c] -> 40/1000, W(*Changes*)-> 6000} 
    
    (*Question 7*)lower /. {Subscript[d, m] -> 22.5/1000, f -> 0.08, 
      Subscript[f, c] -> 0.05, L -> 5/1000, Subscript[\[Alpha], n] -> 0 Degree, 
      Subscript[d, c] -> 40/1000, W(*Changes*)-> 6000, 
      Subscript[M, t](*Changes*)-> 23} 
    (*Question 8*)eff /. {W(*Changes*)-> 4592.508217189424, L -> 5/1000, 
      Subscript[M, t] -> 6.62183}
    
    (*Question 9*)eff /. {W(*Changes*)-> 4592.508217189424, L -> 5/1000, 
      Subscript[M, t] -> 6.62183}
    
    (*Question 10*)raise /. {Subscript[d, m] -> 22.5/1000, f -> 0.08*4/3, 
      Subscript[f, c] -> 0.05*4/3, L -> 5/1000, 
      Subscript[\[Alpha], n] -> 0 Degree, Subscript[d, c] -> 40/1000, 
      W(*Changes*)-> 6000} 
    
    (*Question 11*)raise /. {Subscript[d, m] -> 37/1000, f -> 0.1, 
      Subscript[f, c] -> 0.15, L -> 6/1000, Subscript[\[Alpha], n] -> 14.5 Degree,
       Subscript[d, c] -> 60/1000, W(*Changes*)-> 12500} e here


So basically when I run the command for Question 2, I need the answer from that question to do question 3. The way that I am doing it now is I just manually take the answer for W and paste it into the respective variable for question 3. Is there a way that I can generalize it where in question 3 for the variable that is the answer from the previous one is named as something which the program knows it must take the value from the previous calculation? The numbers which are there now are just examples.

I know my words are all over the place, sorry. I would appreciate any help. If you not understanding me, please ask a question and I will try to clarify myself. Thank you very much.