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

it is contrapositive

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