Calculating Mass Difference in H Atom from Proton & Electron

[knowLittle]

Homework Statement

If an electron and proton (both initially at rest and
far apart) come together to form a hydrogen atom,
13.6 eV of energy is released (mostly as light). By
how much does the mass of an H atom differ from the
sum of the electron and proton masses? What is the
fractional difference ΔM / (m_e + m_p) ?

Homework Equations

E= √( (pc)^2 + (mc^()2)^2 )

E of photon= 13.6 eV

The Attempt at a Solution

Any help on how to proceed?
Can I say that energies of rest masses of proton and electron - 13.6 eV = Energy in H?

Thanks

 

[darkxponent]

Homework Equations

E= √( (pc)^2 + (mc^()2)^2 )

You can assume p=0. Then find the change in total energy!