Substitution method need for home work

-3y = x...so we sub in -3y for x in the other equation

-x + 7y = 70
-(-3y) + 7y = 70
3y + 7y = 70
10y = 70
y = 70/10
y = 7

so we sub in 7 for y in either of the original equations to find x
-3y = x
-3(7) = x
-21 = x

so ur solution is (-21,7)