Help with (AQA) Thermal Physics / Electric Fields A-Level question?

Hi, was just wondering if anyone could discuss or help me understand this question linking thermal physics and electric fields. Managed to get the correct answer to part i, but am still not in full understanding of how I got that answer and would appreciate some help. Also, my answer to part ii was wrong.

Here is the first part of the question:
For a helium-3 nucleus and a helium-4 nucleus to fuse they need to be separated
by no more than 3.5 × 10–15 m.
(i) Calculate the minimum total kinetic energy of the nuclei required for them to
reach a separation of 3.5 × 10–15 m

After some trial and error, I used the electric potential equation, which gave me the correct answer according to the mark scheme. However, I don't fully understand why I did that and how electric potential equates to the minimum required kinetic energy, I was wondering if someone could explain this to me better - I believe that electric potential is in Joules per Coulomb, but the answer was in joules and no conversion was required.
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Second part of the question:
Calculate the temperature at which two nuclei with the average kinetic energy for that temperature would be able to fuse.
Assume that the two nuclei have equal kinetic energy.
For the second part of the question, I equated my answer to part i to
3/2 kT
The mark scheme also used this equation, however they got a much different answer, so I am assuming I have substituted the wrong values in.
Any help would be great

Thank you very much for answering. The value I used in part ii was the (correct) answer to part i (2.62 x10^-13) which I equated to 3/2 kT. Divided part i by 3/2 then constant k (using calc), to find T. My answer was 1.265 x10^10. The correct answer was 6.28 x10^9.