Finding y, which is a bit more difficult.
2x+y=8 ....(a)
3x +4y = 7....(b)
To cancel out x to find y, we need to multiply (a) by -3 and multiply (b) by 2. This is because once we've done that. The x values will be -6x and 6x, which cancel out so you can find y. :D
(a) x -3
-6x + -3y = -24 ....(c) New equation can be called (c)
(b) x 2
6x + 8y = 14 .... (d) New equation can be called (d)
Add (c) and (d)
-6x + -3y + 6x + 8y = -24 + 14
-3y + 8y = -10 The x values cancel out so now you can find y (-6x +6x = 0 aka cancels out)
5y = -10
y = -10/5
y = -2
------------------------> x = 5 and y = -2
Hoped this helped! :D