Use substitution to solve

7x-7y=-7

x+y=13

y=7

x=6

Step-by-step explanation:

7x-7y=-7

x+y=13

rearrange the y

x+y=13

subtract x on both sides

y=-x+13

substitute

7x - 7 (-x+13) = -7

7x+7x+-91=-7

simplify

14x+-91=-7

get rid of the - 91, add 91 to both sides

14x=84

divide 14 from both sides

x=6

Now that we have 6 we can simplify it into the other equation

x+y=13

6+y=13

subtract 6 from both sides

y=7

x=6

Substitute it into the equation to check if both variables are correct

x+y=13

7+6=13

7 (6) - 7 (7) = -7

simplify

42-49=-7

-7=-7