3) Find the perimeter: Add all numbers with the same amount of variables together:
3a + 4a + 5a = 12a
12a is perimeter
4) (3b - 5) + (3b - 5) + b
Add numbers with variables together, and the constants together
3b + 3b + b = 7b
-5 + -5 = -5 - 5 = -10
7b - 10 is the perimeter
hope this helps