Calculate the number of waves made by a Bohr's electron in one complete revolution in its 3rd orbit of H-atom

$(a)\;1\qquad(b)\;3\qquad(c)\;2 \qquad(d)\;4$

What is n there ?

The radius of Bohr's orbit for H-atom
$r_1H=0.529\times10^{-8}cm$
$r_3H=0.529\times 10^{-8}cm\times(3)^{2} cm$
And velocity $u_1 for H-atom = 2.1847\times10^{8}cm/s$
$u_3=\large\frac{u_1}{ n} =\frac{2.1847\times10^{8}}{3}$
since $\lambda=\large\frac{ h}{ mu}$
$\Rightarrow\large\frac{2\times 3.14\times 0.529\times10^{-8}\times 9\times 9.1\times10^{-28}\times 2.1847\times10^{8}}{ 6.626\times10^{-27}\times 3}$
$\Rightarrow 3$
Hence (b) is the correct answer.
edited Jan 23, 2014
Which formula u applied?