see the attached figure to better understand the problem
Step 1
Find the volume of the rectangular prism
The volume of a rectangular prism is equal to
[tex]V=x*6*6\\V=36*x\ units^{3}[/tex]
Step 2
Find the surface area of the rectangular prism
we know that
the surface area is equal to
SA=2*area of the base+perimeter of base*height
area of the base=6*x units^{2}
perimeter of base=2*(6+x)=(12+2*x) units
height=6 units
substitute
SA=2*(6*x)+(12+2*x)*6
SA=12*x+72+12*x-------> SA=(24*x+72) units^{2}
Step 3
equate the value of the volume with the value of the surface area
36*x=(24*x+72)
36*x-24*x=72
12*x=72
x=72/12-------> x=6 units
therefore
the answer is
the value of x is 6 units
