imgur: the simple image sharer

For both a) and b), I'm not sure what to do.

a) It is asking for the length of the diagonal and we are given a formula, A of circle = 38pi m^2

Half of the circle = diagonal

So, should I just divide that formula by 2 and make it into a radical? How do I turn it into a radical if it becomes a decimal number (because of the pi)?

b) I have no clue.