Well, since the Surface Area of a Rectangular Prism = 2ab + 2bc + 2ac. If we separate or variables into a,b,c we should get something that looks a little like this. a=x, b=2x, c=x+8. Now that we have singled out our variables, we can plug it into the equation. Once it is plugged in it should look like this: 2(x)(2x)+2(2x)(x+8)+2(x)(x+8). Now we have to multiply our terms to simplify the expression. Once done you should have an answer like this: [tex] 4x^{2} [/tex]+[tex] 4x^{2} +32x[/tex]+[tex] 2x^{2} +16x[/tex]. Now you combine like terms. After this step, you should have the answer: [tex] 10x^{2}+48x [/tex]
