No. But what I'm going to do is write in the values of 'a', 'b', and 'c' in each expression. Then all you need to do is the multiplication, and you'll have the answer to each one.
13). -2a = -2(-3)
14). 9b = 9(-4)
15). ab = (-3) (-4)
16). -3ac = (-3) (-3) (5)
17). -2c² = -2 (5²)
18). abc = (-3) (-4) (5)
Others:
1). to 7)., and 9). and 10). are all correct
8). 3(-2x) = -6x
11). -6(-3y) = 18y
12). should be negative
