when you get this kind of exercise, you find need to find y or x in one of the exactions and fill it in in the other, however in this exercise the two y's are already given so all you need to do is replace the y in one of the exactions with the other exactions like this:
(keep in mind, you need to keep writing both of the exactions over again, otherwise you'll lose an exaction. and we'll need it later on)
y=-2x+6
y=3x-4
y=-2x+6
-2x+6=3x-4
y=-2x+6
-2x-3x=-4-6
y=-2x+6
-5x=-10
y=-2x+6
x= 2
and now replace the x in the first exaction with the x that we found:
y=-2(2)+6
x=2
y=-4+6
x=2
y=2
x=2