Kaylee found the surface area, in square inches of a rectangular prism by using this formula. 2(5 × 3) + 2(5 × 8) + 2(3 × 8) what is the surface area of the prism, in square inches?

24in with the exponent of 2.

To determine the surface area of a rectangular prism, the Equation is: 
Surface Area  = (length x width + width x height + length height)x 2

The surface area with:
 length of 2(5 x 3), a width of 2(5 x 8), a height of 2(3 x 8)
               SA =  2(15) = 30,  SA = 2(40) = 80, SA = 2(24)= 48, 
                              SA = 30 + 80 + 48
                              SA = 158 square units.

SA = 2LW + 2LH + 2HW
SA = 2(5 x 3) + 2(5 x 8) + 2(3 x 8)
SA = 2(15) + 2(40) + 2(24)
SA = 30 + 80 + 48

SA = 158 in^2

So, your answer is: 158 in^2

Hope that helps!!!