The rectangular prism has measures 6 units by 6 units by x units,
Thus, the volume is 6*6*x = 36x (units cubed)
The surface area of the prism is
2(x*6+x*6+6*6)=2(6x+6x+36)=2(12x+36)=24x +72 (units squared.
36x=24x +72
36x-24x=72
12x=72
x=72/12=6
Answer: x=6