You have two rectangular sides with a total area of:
A=2(10*15)=300 ft^2
You have two triangular sides with a total area of:
A=2(8*12)/2=96 ft^2
And you have a rectangular base with an area of:
A=15*12=180 ft^2
So the total surface area is:
A=300+96+180=576 ft^2
