so elimination
lets say
x+y=10
x+2y=15
if we make the first equation negative and add it to the second we get
-x+x-y+2y=-10+15 or
(x cancels out)
y=5
subsitution
x+3y=7
y=x+1
subsitute y=x+1 for y in the first equation
x+3(x+1)=7
distribute
x+3x+3=7
group like terms
4x+3=7
subtract 3 from both sides
4x=4
divide both sides by 4
x=1
subsitute x=1 into second equation (y=x+1)
y=(1)+1
y=2
