x + y = 3
2x + 4y = 8
This is a system of equations. You can solve it using elimination. Start by multiplying the top equation by -2.
(x * -2) + (y * -2) = (3 * -2)
-2x - 2y = -6
Now add that and the bottom equation. This will cancel out x.
-2x - 2y = -6
+ 2x + 4y = 8
-----------------------
2y = 2
Solve for y.
2y = 2
y = 2/2
y = 1
Now plug 1 in for y in the first equation.
x + y = 3
x + 1 = 3
Solve for x.
x + 1 = 3
x = 3 - 1
x = 2
So x = 2 and y = 1.