Explanation:
the surface area consists of 6 individual areas :
front and back (both are equal)
left and right (both are equal)
top and bottom
front and back are trapezoids.
the area of a trapezoid is
(base 1 + base 2)/2 × h
the bases are the 2 parallel sides.
in our case the area of one trapezoid is
(5 + 19)/2 × 12.1 = 145.2 ft²
front and back together then are 290.4 ft².
left and right are 8×14 rectangles:
8×14 = 112 ft²
together they are 224 ft².
the bottom is a 5×8 rectangle :
5×8 = 40 ft²
the top is a 19×8 rectangle :
19×8 = 152 ft²
so, the total surface area is
290.4 + 224 + 40 + 152 = 706.4 ft²