Question 34229
[1]  x - 3y = 25
[2]  -6x - 4y =-18

Use the first equation and solve for x:
[1] x = 3y + 25

Then take what x equals in the first equation and substitute it for x in [2]:
-6x - 4y =-18
-6(3y + 25) -4y = -18

Now solve that equation for y. 
-6(3y + 25) -4y = -18
-18y - 150 - 4y = -18
-22y = 132
y = -6

Take that y = -6 and put it back into [1].
x = 3y + 25
x = 3(-6) + 25
x = -18 + 25
x= 7

Always check both solutions in both equations:
[1]  7 - 3(-6) = 25 7+ 18=25  CHECK
[2]  -6(7) - 4(-6)=-18 -42 + 24 = =18 CHECK

x= 7, y=-6