A photon behaves as if it had a mass equal to -

$\frac{hv}{c}$ $\frac{hv}{c^2}$ $\frac{c^2}{hv}$ $hvc$

$\frac{hv}{c^2}$

$E=mc^2$ $m=\frac{E}{c^2}=\frac{hv}{c^2}$