Write a function describing the relationship of the given variables.


$\displaystyle {h}$ varies directly with the square root of $\displaystyle {d}$ and when $\displaystyle {d}={36}$, $\displaystyle {h}={78}$. Find $\displaystyle {d}$ when $\displaystyle {h}={39}$


$\displaystyle {d}=$Preview Question 6