Answer:
See the explanation below.
Step-by-step explanation:

Starting from 
By putting
we have:

Answer:
c.20
Step-by-step explanation:
first step:24÷3=8
final step: 12+8=20
Answer:
672 sq cm
Step-by-step explanation:
Each triangular base is 1/2 (12 * 8) or 48, making them = 96.
One of the sides is 12 x 18 = 216
The other 2 sides are 10 x 18 = 180 x 2 = 360
Add them all together to get 672 sq cm