Using the tool
Read Variables, then type what you wrote for variables. Parentheses and units are the usual sources of mismatch.
Change one input
Change one input at a time. If the output jumps more than you expected, that input was doing more work in variables than you thought.
Parentheses
Write 3(x + 2) on paper. Enter it with parentheses so the tool multiplies 3 by the whole sum, not only by x.
Match
Written work Tool output
Side-by-side check
Core lesson
Related: Variables. Use the calculator with your own numbers when the example is not close to your case.