The second equation gives an expression for y that can be used directly in the first equation.
... 8x + 5(x+7) = 9 . . . . . substitute for y
... 13x + 35 = 9 . . . . . . . simplify
... 13x = -26 . . . . . . . . . . add -35
... x = -2 . . . . . . . . . . . . . divide by the coefficient of x
... y = -2 + 7 = 5
The solution is ...
... B. (-2, 5)
