x/(x - 9) = 4/7

(x + y)/(x - y) = 5/3

I'm assuming you're trying to solve this system of equations.

x = 4/7*(x-9)

7x = 4*(x - 9)

7x = 4x - 36

36 = -3x

x = -12 -- (1)

(x + y)/(x - y) = 5/3

x + y = 5/3*(x - y)

x + y = 5/3x - 5/3y

y = (2x)/3 - (5y)/3

3y = 2x - 5y

8y = 2x

y = x/4

But, from (1), we can substitute x in for y;

y = (-12)/4

y = -3

Thus, we have (-12, -3)