Substitution for 4x+y=9 and y=-7

4x + y = 9

y = - 7

Plug it in:

4x - 7 = 9

Add 7 to both sides:

4x = 16

Divide 4 to both sides:

x = 4

Plug this back into the equation:

4x + y = 9

4 (4) + y = 9

16 + y = 9

Subtract 16 to both sides:

y = - 7

So our solution is (4, - 7)

{y=-7

{4x+y=9 Substitute y.

4x + (-7) = 9

4x-7=9 / + 7

4x=16 / : 4

x=4

Solution; (4; - 7)