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