4x+5y=23
4x-y=5
Notice that the second equation can be rearranged as :
4x = 5 + y
And substituting this into the first equation for 4x, we have
5 + y + 5y = 23
5 + 6y = 23 subtract 5 from both sides
6y = 18 divide both sides by 6
y = 3
So
4x = 5 + y
4x = 5 + 3
4x = 8 divide both sides by 4
x = 2
So (x , y) = ( 2, 3)