How do you find a and b for the following?

x+2y=8

x-2y=4       add the equations and we obtain :

2x  = 12      divide both sides by 2

x = 6

And substituting this into either equation, we can find y

6 + 2y  = 8     subtract 6 from both sides

2y = 2           divide both sides by 2

y = 1

So....(x , y)   = (6 , 1)