Question

How do you solve the system of equations `x- y = 15` and `3x + 10y = - 20`?

Answer 1

Put `x=15+y` in the second equation. And then `x=10` and `y=-5`

Explanation:

`3(15+y)+10y=-20`
`45+3y+10y=-20`
`13y=-65`
`y=-5`

And x was `=15+y`
Yielding `x=15-5=10`
`x=10`