Each bag of popcorn costs $2. 5
You can solve it by creating an equation. This one can be:
40 -12x = 10
Undo the operation.
40 -12x = 10
-40 -12x = 10 -40
Eliminate the 40. This will live you with the following.
-12x = -30
Divide -12x by -12. Do the same with the -30
-12x = -30/ -12
This will give you the answer.
x = 2.5