Question 1208739
The volume:
{{{27=(1/4)((2x+6)(2x+10)-60)}}}


{{{27=(1/4)(2*2)((x+3)(x+5)-15)}}}

{{{27=(x+3)(x+5)-15}}}

{{{42=(x+3)(x+5)}}}

{{{x^2+8x+15=42}}}

{{{x^2+8x=27}}},  a couple of those steps were not necessary

{{{x^2+8x-27=0}}}

{{{x=(-8+- sqrt(64+4*27))/2}}}

{{{x=-4+- sqrt(43)}}}
Take the positive form.