GCSE Physics: Nuclear Reactions/Nuclear Physics-Please help!?

Ok, the initial element you're dealing with is Uranium, which has 92 protons and a total of 238 nucleons (as denoted by the notation). A nucleon is either a proton or a neutron, so to find the number of neutrons, just subtract 92 (number of protons) from 238 (number of nucleons) which equals 146 neutrons.