Take into account that the lateral faces are 3, and sum the area of such faces.
The area of the rectagular face is:
A1 = (6 in)(10 in) = 60 in²
The area of the other two rectagles is:
A2 = (8 in)(10 in) = 80 in²
A3 = (10 in)(10 in) = 100 in²
Then, the total surface area is:
AT = A1 + A2 + A3
AT = 60 in² + 80 in² + 100 in²
AT = 240 in²
