For which structure (s) does the electron-bearing carbon atom have a formal charge of zero

Formal charge can be calculated from the following formula

Formal charge = valency of central atom - (number of lone pair of electrons + number of covalent bonds)

a) for methylene:

Formal charge = 4 - (2 + 2) = 0

b) For methyl free radical

Formal charge = 4 - (3 + 1) = 0