Answer:
(d) 18 inches
Explanation:
You want the base length of one of two identical triangles left over when the center rectangle of 240 in² is removed from an isosceles trapezoid of area 600 in² and height 20 in.
Solution
Please refer to the attached figure.
After the given rectangle of 240 square inches is removed from the total area, the remaining two identical triangles can be rearranged to form a rectangle of area 600 -240 = 360 square inches, and height 20 inches.
The base of that rectangle is ...
A = BH
B = A/H = (360 in²)/(20 in) = 18 in
The base of each triangle is 18 inches.