Use elimination to solve each system of equations. x+y=2 -3x+4y=15

First, we have to make one of the x's have the same coefficient so they can cancel each other out (or eliminate)

3(x+y) = 3(2)
you're going to have to do it to both sides to keep it balanced

3x+3y=6

now line them up and add them

     3x+3y= 6
+ (-3x+4y=15)

since the 3x and -3x add up to 0x and cancels each other, you're left with
7y = 21

divide both sides by 7

y=3

plug in the y into one of the original equations

x+y=2
x + 3 = 2

subtract 3 from both sides

x = -1

x = -1 , y = 3

Hmmm i had this before , give me a sec