#### Answer

139 AM photons.

#### Work Step by Step

Recall the equation E= hν, where E is the energy, h is Planck's constant and ν is the frequency.
Energy of one FM photon =h$(91.9×10^{6}s^{-1})$
Energy of one AM photon= h($665×10^{3}s^{-1}$)
Number of AM photons needed= Energy of one FM photon÷ Energy of one AM photon =
$\frac{h(91.9×10^{6}s^{-1})}{h(665×10^{3}s^{-1})}$ = $\frac{91.9×10^{6}}{665×10^{3}}\approx138.2$
Since the number of protons cannot be a fraction, we need 139 photons.