What about these types of radicals?

I have only about fifty more to do at the moment and am struggling on a few more.

First problem not sure I really get this type of one

Use rational exponents to simplify each expression.

8

√x^4

Second is to simplify the indicated operation.

3 3

√5x^2 * √10y

Third is:solving this radical equation:

√x+9 - √x-7=2

Fourth is:perform indicated operation. Write in the form of a + bi

(5-3i) - (6-9i)

would I do the foil on this where 30-18i+18i okay no that ones is wrong.

Question on my second problem

The problem is

3 3

√5x^2 * √ 10y

The book is saying 3

√ 50x^2y as an answer but I see you have 1/3 in there. Where does that come in? I think I am more confused??