A rain gutter is to be constructed of aluminum sheets 12 inches wide. after marking off a length of 4 inches from each edge, this length is bent up at an angle θ. the area of the opening may be expressed as the function: a(θ) = 16 sin θ ⋅ (cos θ 1). if θ = 30°, what is the area of the opening?

a. 14.9 in²
b. 16.0 in²
c. 19.3 in²
d. 20.8 in²