Suppose a Trough with Trapezoidal Cross Sections Is Formed by Turning

Multiple Choice

Suppose a trough with trapezoidal cross sections is formed by turning up the edges of a 30-inch-wide sheet of aluminum (see figure) . Find the cross section of maximum area.

A) $x = 12 ; \theta = 45 ^ { \circ }$
B) $x = 20 ; \theta = 55 ^ { \circ }$
C) $x = 10 ; \theta = 45 ^ { \circ }$
D) $x = 10 ; \theta = 60 ^ { \circ }$
E) $x = 20 ; \theta = 60 ^ { \circ }$