Calculate the radius of the nth orbit

Calculate the radius of the nth orbit
(a) $\sqrt{\frac{nh}{2\pi eB}}$ (b) $\sqrt{\frac{nheB}{2\pi}}$ (c) $\sqrt{\frac{nhe}{2\pi B}}$ (d) $\sqrt{\frac{nhB}{2\pi e}}$

Aswer:(a) $\sqrt{\frac{nh}{2\pi eB}}$