Take into account that the figure has six faces, two of them with an area of:
A1 = (5 ft)(10 ft) = 50 ft²
another two of them with an area of:
A2 = (20 ft)(5 ft) = 100 ft²
and another two with an area of:
A3 = (20 ft)(10 ft) = 200 ft
The total surface area is given by:
AT = 2(A1) + 2(A2) + 2(A3)
replace the values of the parameters:
AT = 2(50 ft²) + 2(100 ft²) + 2(200 ft²)
AT = 100 ft² + 200 ft² + 400 ft²
AT = 700 ft²
Hence, the surface area of the given figure is 700 ft²