I will show you the process, but you need to do the rest.

The definition of variance with a single random variable is .

After expanding and eliminating you will get

For two variable, you substiute X with XY, it becomes

----eq(1)

where and --------------------eq(2)

When X and Y are independent ------eq(3)

Substitute eq(2) and eq(3) into eq(1). You should get the final form you find in you book.