um, you are forgetting something here...

multiply through by 2a, you will get2/a = 1/2 + 3/a

4 = a + 6

can you continue?

or perhaps an easier way for you to follow is to get all a's on one side. so you would begin by subtracting 3/a from both sides to get:

2/a - 3/a = 1/2

adding the fractions on the left becomes

-1/a = 1/2

now what?