Hey there!
We can tell from the information we are given that the sum of protons and neutrons is 13, there is 6 protons since it is a carbon atom, and there is no charge which means the number of protons is equal to the number of electrons.
6 + n = 13
n = 7
The number of protons is equal to the number of electrons, so there is 6 electrons.
The isotope 13C has 6 protons, 6 electrons, and 7 neutrons.
Hope this helps!
