Suppose a revenue function is given by:

$\displaystyle {R}{\left({q}\right)}=-{q}^{{3}}+{159}{q}$
Revenue is maximized for a value of $\displaystyle {q}$ that takes the form $\displaystyle {q}=\sqrt{{{N}}}$, where $\displaystyle {N}$ is a whole number (no decimals or fractions). Find the value of $\displaystyle {N}$.

$\displaystyle {N}=$