Question

{y = 3x -1
{x-y = - 9

Answer 1

always make sure both the equations have equal notations so 3x-y=1 and x-y=0
after the that u may use the normal simultaneous eqn and find values of x and y

Answer 2

Here, substitute the value of y from equation 1 into equation 2, 
x - y = -9
x - (3x - 1) = -9
x - 3x + 1 = -9
-2x = -9 - 1
x = -10/-2
x = 5

Now, substitute the value in 1st equation, 
y = 3(5) - 1 
y = 15 -1 = 14

In short, Your Answer would be: (5, 14)

Hope this helps!