Question

How would you solve this problem?

Answer 1

Subtract the two equations.
-y = -7
y = 7
Plug 7 back in to either equation and solve for x.
x + 3(7) = 18
x + 21 = 18
Subtract 21 from both sides
x = -3
(-3,7)
CHECK
-3 + 3(7) = 18
-3 + 4(7) = 25

Answer 2

You could solve using substitution or elimination.
I'm going to use elimination.
Multiply the whole top equation by -1 so that you are able to cancel out the x. -x-3y=-18
Now cancel out the x in both equations to make an equation with only one variable. Combine like terms as well
-x-3y=-18
x+4y=25.........y=7

Now plug in y into one of the original equations. x+3(7)=18
x+21=18 Subtract 21 from both sides
x=-3