I need help!!!! How do you solve systems using substitution?????

Solving systems of equations requires you to solve one equation for a variable. Then plug that equation into the second equation, and solve. Here's an example:

Equation 1: y = 2x + 5
Equation 2: -5x = y + 2

Since you already know from the first equation that y = 2x + 5, put 2x + 5 into the second equation, and solve.

-5x = (2x + 5) + 2
-5x = 2x + 7
-7x = 7
x = -1

Now plug in x to one equation to solve for y:

y = 2(-1) + 5
y = 3