#### Answer

(a) $220~ft^2$
(b) $1408

#### Work Step by Step

(a) We can find the area of the upper section:
$A_1 = (12~ft)(10~ft) = 120~ft^2$
We can find the area of the lower section:
$A_2 = (10~ft)(10~ft) = 100~ft^2$
The total area is $220~ft^2$
(b) We can find the cost:
$cost = (\$6.40/ft^2)(220~ft^2) = \$1408$