Two neutrons are trapped in an infinite square well with a width of 2.0 fm. The minimum total energy the system can have is 255.7 MeV. This is calculated by finding the individual energy levels of each neutron using the particle in a box model and then summing them. The first neutron has an energy of 51.14 MeV and the second neutron has an energy of 204.56 MeV, giving a total minimum energy of 255.7 MeV.