2(2ax-y)=3ax-4y
4ax-2y=3ax-4y
Move 3ax from the right to the left. You do so by subtracting 3ax from both sides. Once doing so, you should have:
ax-2y=-4y
Isolate ax. You do so by adding (-2y) to both sides. After doing so, you should have:
ax=-2y
To isolate y by itself, you divide everything by -2, thus, equaling y= ax/-2