I used to have trouble with this kind of equation too! I gotcha!
The first one is 12x-17 because if you have PR, which is the total of the entire line, you will be able to subtract PQ from it to get the equation for QR
(15x-11)-(3x+6)=12x-17
For the second problem i will draw it out for you:
In the picture, i show you how to get the perimeter. For this specific question, you can get rid of the answers to find out that the answer is D, because area is measured in units CUBED.
Good luck out there and Stay Safe!
