#### Answer

40 $ft^{2}$

#### Work Step by Step

The area of a trapezoid whose bases have lengths b1 and b2 and altitude has length of h is given by
A = $\frac{1}{2}$*h(b1+b2)
Lets take b1 = BC = 13ft
b2 =AD = 7ft
h = 4 ft
Therefore A = $\frac{1}{2}$*4* (13+7)
= 2*(20) = 40 $ft^{2}$