Solve the following problem given below:

Problem: An alpha particle is a nucleus of Helium. It has twice the charge and four times the mass of the proton (mp = 1.67 x 10^-27 kg, c = 1.60 x 10^-19 C). A proton and an alpha particle headed directly toward each other, had each initial speed of 0.0030c when they were far away. Here, as is customary when describing processes involving nuclear targets, the speed is expressed as a fraction of the speed of light, c = 3.0 x 10⁺⁸ m/s.

What is their distance of closest approach?

Any help I can get on this problem is greatly appreciated! I'm not too familiar with this problem. Hint: There are two conserved quantities. Make use of both.