Assuming you meant
[tex]y = \frac{7}{ \sqrt{8x+10} } [/tex]
Then you can compose the function g(x)
[tex]g(x)= \sqrt{8x+10} [/tex]
With the function
[tex]f(x)= \frac{7}{x} [/tex]
Because f (g(x) ) means that you first find (calculte) [tex] \sqrt{8x+10} [/tex] and second you divide 7 by g(x) to obtain 7 / [√(8x+10) ].