multiply first equaton by 2 and add to the other equation
6x+6y=12
5x-6y=15 +
11x+0y=27
11x=27
divide both sides by 11
x=27/11
sub back
3x+3y=6
divide both sides by 3
x+y=2
(27/11)+y=2
2 and 5/11+y=2
minus 2 and 5/11 both sides
y=-5/11
x=27/11
y=-5/11
(27/11,-5/11)