5x+3y=39
x+y=3
we will eliminate the y terms first
multiply bottom equation by -3
-3x-3y=-9
add this to the first equation
5x-3x+3y-3y=39-9
2x+0=30
divide both sdies by 2
x=15
subsitute into second equation
x+y=3
15+y=3
subtract 15 from both sdies
y=-12
x=15
y=-12