Rearranging formula

I need some help with rearranging formula.
the first one is. Make r the subject of the formula:
H = w^2 / 2g (R^2 - r^2)
and the second one is. Make a the subject of the formula:
T = (Sqrt pbh / 4 + a^2)

Please give some working along with the answer
Thanks in advance

Are you still stuck? What have you tried?

I've rearranged the second one but I'm stuck on the first one I'm not sure how to get rid of the brackets and all of the powers :/

yes

If you multiply both sides of equation by $R^2-r^2$ and divide both sides by $H$ you get
$\displaystyle R^2-r^2=\frac{w^2}{2gH}$.
Can you do anything from here?