Answer :
It helps to imagine the variable a sort of as a unit. Like with 5 minus 12 lemons, it has no bearings on the addition/subtraction here.
Factor out a and subtract.
[tex]5a-12a \\ (5-12)a \\ \boxed{-7a}[/tex]
Factor out a and subtract.
[tex]5a-12a \\ (5-12)a \\ \boxed{-7a}[/tex]
