Question

Y = 3x + 15
3x + 3y = 9

Answer 1

`\Large\boxed{x=-3}`
`\Large\boxed{y=6}`

Explanation:

Given the system of equations

`1)~y=3x+15`

`2)~3x+3y=9`

Divide 3 on both sides of the 2) equation

`3x+3y=9`

`3x/3+3y/3=9/3`

`x+y=3`

Current system

`1)~y=3x+15`

`2)~x+y=3`

Substitute 1) equation into the 2) equation

`x+(3x+15)=3`

Combine like terms

`x+3x+15=3`

`4x+15=3`

Subtract 15 on both sides

`4x+15-15=3-15`

`4x=-12`

Divide 4 on both sides

`4x/4=-12/4`

`\Large\boxed{x=-3}`

Substitute the x value into one of the equations to find the y value

`y=3x+15`

`y=3(-3)+15`

`y=-9+15`

`\Large\boxed{y=6}`

Hope this helps!! :)

Please let me know if you have any questions