g(9/7)=7x+5

Was this problem originally:    g(x) = 7x+ 5       and you were supposed to find g(9/7) ?

If so:    replace 9/7 in for x throughout the original expression:

                                           g(9/7) = 7(9/7) + 5                    (multiply 7 times 9/7 to get 9)

                           --->          g(9/7) = 9 + 5

                           --->          g(9/7) = 14

You need to solve for one variable first, b/c you cant combine the two variables in any way.