By definition of inverse function,
[tex]F\left(F^{-1}(x)\right) = x[/tex]
so that
[tex]5F^{-1}(x) - 6 = x[/tex]
[tex]5F^{-1}(x) = x + 6[/tex]
[tex]F^{-1}(x) = \dfrac{x + 6}5[/tex]
Similarly,
[tex]G\left(G^{-1}(x)\right) = G^{-1}(x) - 4 = x \implies G^{-1}(x) = x+4[/tex]
Then the inverse of the composition [tex]F\circ G[/tex] is such that
[tex]\left(F \circ G\right) \left((F \circ G)^{-1}(x)\right) = x[/tex]
By definition of composition,
[tex](F\circ G)(x) = F(G(x))[/tex]
Applying [tex](F\circ G)^{-1}[/tex] to this recovers x, and this involves first inverting F, then G:
[tex](F\circ G)^{-1}(x) = G^{-1}\left(F^{-1}(x)\right)[/tex]
So, we find
[tex](F\circ G)^{-1}(x) = G^{-1}\left(F^{-1}(x)\right) = G^{-1}\left(\dfrac{x+6}5\right) = \dfrac{x+6}5 + 4 = \boxed{\dfrac{x+26}5}[/tex]
