Solve for - x - 3y = - 21 and 4x - y = - 7

4x - y = - 7

4x - y+y = - 7+y

4x=-7+y

4x+7=-7+y+7

4x+7=y

- x - 3y = - 21

- x - 3(4x+7) = - 21

- x - 3(4x) (-3)(+7) = - 21

-x -12x-21=-21

-13x-21=-21

-13x-21+21=-21+21

-13x=0

-13x/-13=0/-13

x=0

4x+7=y

4(0)+7=y

0+7=y

7=y