According to the statements the number of electrons is 150, then
e = 150
But there is a positive charge of +22e, then the number of protons would be
p = 150+172
If the mass of the electrons is
[tex]m_e = 9.11*10^{-31} kg[/tex]
And the mass of the protong is
[tex]m_p = 1.673*10^{-27}kg[/tex]
We have that the total mass of the system would be
[tex]m = e*m_e +pm_p[/tex]
[tex]m = 150 * (9.11*10^{-31})+170(1.673*10^{-27})[/tex]
[tex]m = 2.84547*10^{-25} kg[/tex]
