Mystified by inability to find info to do what seems really basic [closed]

Question

Trying to do some basic algebra here, have input 12 expressions. I would like to label the output so that I can connect the outputs to the context of the inputs, within the output line.

Having no luck finding anything related to this via web search, or searchboxes within Mathematica's documentation.

Generally when I do find something that appears relevant by such searches and try it, the error messages generated do not convey anything I can extract any sense from.

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Incorporating Nasser's comment:

additional info from user5997 via email to help others:

Long list of expressions in one input cell. Evaluate notebook. Want to quickly find output for nth input of m total lines. Currently settling for adding semicolon at end of all other input lines. Would really like to preface output with string representing input expression, line by line, so sort of interleaving output line with corresponding input code. Not sure if this makes it any clearer. I do appreciate the help

Answer 1

Each of the methods I described here are adaptable, as the question that answers is a more specific version of this one. Illustrating the first:

$Pre = Function[expr, Print["Input: ", HoldForm@expr]; expr, HoldAll];

Now evaluating these lines in a single cell:

2 + 2
a^2 + 15*4^2
Sin[2 Pi]
Log10[100/10]