Answer
$a = 16.6$ $ inches$
Work Step by Step
The offset distance $x$ is simply one of the side of the pipe.
We have the sides:
$c = 18 in$
$b = 7 in$
and $a$ would be our offset distance $x$.
We use the Pythagorean theorem to find $x$:
$a^2+b^2=c^2$
$x=a=\sqrt{c^2-b^2}$
$x = \sqrt {(18in)^{2} - (7in)^{2}} = 16.6in$
