How do you solve (y=x-4)=(2x+y=5) using substitution?

Y = x-4

2x + y = 5
2x + (x-4) = 5
3x - 4 = 5
3x = 9
x = 3

Substitution is done by replacing a variable for an equation. In this case:

2x+y=5
would be
2x+(x-4)=5 (If you notice, you see that the value of x was replaced in the main equation)

Then you would solve as normal.

2x+x-4=5
3x-4=5
3x=9
x=3

Then we can plug in x for any one of the equations to find y.
y=x-4
y=3-4
y=-1

So the solution is x=3 and y=-1.

:)