How do i do #8? pleas explain you

12 inches to 36 inchesif it is increasing (going from a smaller number to a larger number), then it is a percent increase

increase = (new number - original number) / original number...* 100
               = (36 - 12) / 12* 100
               = 24/12 * 100
               = 2 * 100
               = 200% increase <==

now as far as a decrease (when it goes from a larger number to a smaller number) the formula is : 
decrease = (original number - new number) / original number..* 100

a.bh/2

b.b=A×2/h

c.12

Step-by-step explanation: