3x+y=17
x+3y=-1
Multiply 3 to each side
x*3+3y*3=-1*3
3x+9y=-3
Use substitute property
3x+9y=-3
-
3x+y=17
=
8y=-20
Divided 8 to each side
8y/8=-20/8
y=-2.5
3x+y=17
Substitute y with -2.5
3x+(-2.5)=17
3x-2.5=17
Add 2.5 to each side
3x-2.5+2.5=17+2.5
3x=19.5
Divided 3 to each side
3x/3=19.5/3
x=6.5
Next,
3x+3y
Substitute x with 6.5 and y with -2.5
3(6.5)+3(-2.5)
=19.5-7.5
=12 is your final answer. Hope it help!