math

$R^3=\sqrt{4hp}\\ \text{Square both sides to remove square root}\\ (R^3)^2=(\sqrt{4hp})^2\\ R^6=4hp\\ \text{Divide 4h to isolate p}\\ \frac{R^6}{4h}=p$

For line 3, one of the law of exponents state:
$(x^a)^b=x^{ab}$