Solve the following system of equations by using the substit

Solve the following system of equations by using the substitution method.
x = y + 3
2x + y = 9

what we need to do is to use one of the equations to give us enoguh information to solve the other. For example, we have,

x = y+3

Knowing this, we can replace all the x in the second equation with y+3,

2(y+3) + y = 9

Notice that we now only have to solve for one variable - y - instead of x and y. This gives,
3y + 6 = 9
3y = 3
y = 1

Now that we have a value for y, we can substitute it into your equations to solve for x,

x = y + 3
x = (1) + 3
x = 4

Notice that y = 4 and x = 1 solves both of your equations at the same time.