The others already have pointed out the problem of your code. But I think it's not bad to say that using 1-D Math input typing usually avoids encountering such mistakes. To type your code in 1-D Math input mode, you should use
* whenever you have a multiplication. For substitution in your code, I prefer to use
ReplaceAll command. And in case your
Solve gives more than one solution, let's say you have a degree two polynomial equation and it gives two different solutions, then you need to tell Mathematica to choose which solution to substitute in your expression. So I prefer to type
sol[] which means the first element of the list of solutions. If you avoid mentioning the index of the solution that you want, then Mathematica will give you a list containing result of the substitution for each of the solutions. So anyway, your code written in 1-D Math input format and my taste will be as the following.
Running it, you will get the following result.