Answer:
68cm^2
Explanation:
Well there's not much to explain - the problem statement does it for us.
The surface area is equal to the sum of areas of the walls. There's 2 l*w walls, 2 l*h walls and 2 h*w walls.
SA = 2*l*h + 2*l*w + 2*h*w
SA = 2*4cm*6cm + 2*4cm*1cm + 2*6cm*1cm = 48cm^2 + 8cm^2 + 12cm^2 = 68cm^2