Answer:
6 inches
Step-by-step explanation:
Area = (base1 + base2)/2 · height
base1 = b
base2= 8
height = 3
Area = 21
21 = (b+8)/2 ·3
21 = 3(b+8)/2
multiply both sides by 2
42 = 3(b+8)
divide both sides by 3
14 = b+8
subtract 8 from both sides
b = 6 in
