1. The problem statement, all variables and given/known data h/(mc) = ? where m is the mass of an electron 2. Relevant equations 3. The attempt at a solution h = 4.136*10^-15 eV*s m = 0.511 MeV/c^2 c = 299792458 m/s So m*c (as long as I remember to multiply by 10^6) gives units of eV/c So h/(mc) gives units of s*c Using the values I've written here, I would get h/(mc) = 2.6998*10^-29 s*c But c has units of m/s, so I can get units of m by multiplying by the numerical value of c, right? Then I multiply by 10^9 to get units of nm, and I get h/(mc) = 8.09*10^-12 nm But this is wrong, because the answer is 0.002426 nm. I can't believe I can't do a simple plug-in problem, but, well, it should be easy enough to help me with.