The conversion factor to use in this case is:
charge / mass = 5.4 x 10^6 z / w
We are given that:
charge = 4.5 x 10^−15 z
Therefore the mass is calculated by combining the two equations:
4.5 x 10^−15 z / mass = 5.4 x 10^6 z / w
mass = 8.33 x 10^-22 w