Question 1016194
6'x10' is 72"x120"

This is similar to the "picture frame" problems with a couple differences. 

27 cu ft is 27*12x12x12 = 46656 cu inches. With a 3" depth, we have 15552 square inches of boarder.

The garden is 72x120= 8640 square inches. 

When we add the border, we get 

(72+2x)(120+2x)=24192 (the sum of 8640+15552)

{{{4X^2+384x+8640=24192}}}

{{{4X^2+384x-15552=0}}}

Quadratic formula gives 30.69 as the positive solution. Please double check this. Not all problems offer a nice integer answer, but I may have an error somewhere.