3x+y=17
4x-y=18
4x-y=18
subtract 18 from both sides
4x-y-18=0
add y to both sides
4x-18=y
subsitute 4x-18 for y in first equation
3x+(4x-18)=17
7x-18=17
add 18 to both sides
7x=35
divide both sides by 7
x=5
subsitute
y=4x-18
y=4(5)-18
y=20-18
y=2
x=5
y=2