math
posted by Thomas .
The area of rectangle ACED is 80 square centimeters, and the area of triangle BCE is 30 square centimeters, If AD = 4 centimeters, then what is AB ?
a. 5 cm
b. 10 cm
c. 15 cm
d. 20 cm
e. 25 cm
please answer and explain

AC*AD = 80, so AC = 20
AD=CE=4
CE*BC/2 = 30, so BC=15
AB+BC=20, so AB=5