Use the formula for the surface area of a square pyramid to solve for the slant height if the length of the base is 40 in. and

SA equals 2, 800 in.

The formula for the surface area of a square pyramid is:

SA = Base Area + (1/2) * Perimeter of Base * Slant Height

Given that the length of the base is 40 in. and the surface area is 2,800 in., we can substitute these values into the formula:

2,800 = (40^2) + (1/2)*(4*40)*Slant Height

Simplifying:

2,800 = 1,600 + 80*Slant Height

Subtracting 1,600 from both sides:

1,200 = 80*Slant Height

Dividing both sides by 80:

15 = Slant Height

Therefore, the slant height is 15 inches.