I tried approaching this as a normal rectangle, but my answer doesn't seem to be in the options. Here's the question -
An open rectangular tank: 4m long, 3m wide and 4m high is made out of a thin metal sheet. Find the area of the metal sheet used in its construction.
Sine, the tank is open say at the top then surface area of the tank $$=(\text{total surface area of lateral walls of the tank })+\text{(area of rectangular base of the tank})$$
$$=2(\text{(length)}\times(\text{height})+\text{(width)}\times(\text{height}))+\text{(length)}\times(\text{width} )$$
Area of total surface of the tank $$=2(4\times 4+3\times 4)+3\times 4=2(28)+12=68 \ m^2$$