How many neutrons does element x have if it's atomic number is 58 and it's mass number is 153

Mass number means corresponds to the nucleus i.e the number of neutrons and protons.
The atomic number correspond to the protons ( also electrons in stable atoms ).
So when we take away the atomic number from the mass number we get the number of neutrons.
153 - 58 = 95 of neutrons.
Hope this helps :).