Solve the system using substitution. Show all your work.

4x+5y=7

y=3x+9

Since we know what y is, it is 3x+9, we can substitute 3x+9 in for y in the first equation

4x+5y=7

Substitute 3x+9 in

4x+5 (3x+9) = 7

Distribute the 5

4x + 5*3x + 5*9=7

(4x+15x) + 45=7

Combine like terms

19x=-38

Divide both sides by 19

x = - 2

Now we know x, and have to find y. Substitute - 2 in for x in either of the equations

y=3x+9

y=3 (-2) + 9

y=-6+9

y=3

x = - 2, y = 3

Step-by-step explanation:

Solve for the first variable in one of the equations, then substitute the result into the other equation.