Answer
See below
Work Step by Step
Given: $f(x)=6x^2+1, x\geq0\\g(x)=(\frac{x-1}{6})^{1/2}$
Obtain: $g(f(x))=g(6x^2+1)=(\frac{6x^2+1-1}{6})^{1/2}=(\frac{6x^2}{6})^{1/2}=(x^2)^{1/2}=\sqrt x^2=x$
$f(g(x))=f((\frac{x-1}{6})^{1/2})=6((\frac{x-1}{6})^{1/2})^2+1=6.\frac{x-1}{6}+1=x-1+1=x$
$g(f(x))=f(g(x))=x$