Give the nuclide symbol for an atom that has mass number 64 and 35 neutrons.

The mass number represents the summation of the number of protons and the number of neutrons in the nucleus of an atom.
We are given that the mass number is 64 and that the number of neutrons is 35. Therefore:
number of protons = 64 - 35 = 29 protons

In ground state, number of protons in an atom is equal to the number of electrons. Therefore,
number of electrons = 29 electron

Using the periodic table, we will find that the element that has 29 electrons in ground state is copper.
The nuclide symbol of copper is shown in the attached image.