Answer:
a) 30 cm
b) 20 cm
Step-by-step explanation:
Rectangle B's perimeter is 10+10+5+5 which is 30
Square C's perimeter is 5+5+5+5 which is 20
Your answer is -5.
This is because, if you expand the single bracket, you get -6x -3a, and since the other side of the equals sign is -6x + 15, then you need to do 15 ÷ -3 = -5.
I hope this helps!
