F(x)=3 domain: negative infinity, positive infinity range: 3
g(x)=x+7 domain: - infinity, + infinity range: - infinity, + infinity

We effectively rewrite the equation as

In order for the LHS to be defined, we need to restrict
, or
. Now, the LHS will vanish when the numerator is 0, which happens for

This value is indeed smaller than 4, so the solution is
.
Here is my answer, hope to help you
Your total volume would be 150 cubic feet and the weight would be .1