Question

How do you solve `3x+y=9` and `2x+y=4`?

Answer 1

Subtract the second equation from the first to get `x=5`, then substitute that into either equation and rearrange to find `y=-6`

Explanation:

Subtracting the second equation from the first we find:

`x = (3x+y)-(2x+y) = 9 - 4 = 5`

Then substitute `x=5` in the second equation to get:

`4 = 2*5+y = 10 + y`

Subtract `10` from both ends to get:

`y = 4 - 10 = -6`