Answer:

Step-by-step explanation:
see the attached figure , to better understand the problem
we have

where
A(b) ---> is the trapezoid's area
b ---> is the other base value
Solve the equation for b
That means ----> isolate the variable b
Divide 12 by 2 right side

Divide by 6 both sides

subtract 9 both sides

Rewrite

Convert to function notation
