Functions

For some a, b, c \(\in\mathbb{N}\), let \(f(x) = ax - 3\) and \(\mathrm{g(x)=x^b+c,x\in\mathbb{R}}\). If \({(fog)^{ - 1}}(x) = {\left( {{{x - 7} \over 2}} \right)^{1/3}}\), then \((fog)(ac) + (gof)(b)\) is equal to ____________.