Question

How do you solve `3x+5y=36` and `-9x+y=36` using substitution?

Answer 1

`y=4`
`x=-4/3`

Explanation:

`color(red)(3x+5y)=color(green)(36)" (1)"`
`color(red)(-9x+y)=color(green)(36)`
`color(red)(3x+5y=-9x+y)`
`3x+9x=y-5y`
`12x=-4y`
`x=-(4y)/12`
`x=-y/3" "(2)`
`"let's use the equation (1)"`
`3(-y/3)+5y=36`
`-y+5y=36`
`4y=36`
`y=36/9" "y=4`
`"using the equation (2):"`
`x=-4/3`