According to the Element Tables, molybdenum has atomic number (Z) equal to 42, and tin has atomic number 50. So the total number of protons on the right side is 92 (50 + 42), which equals the number of protons in the uranium nucleus.
The number of neutrons in these isotopes is:
An alternate calculation, once it's determined that the protons balance, is to just compare the mass numbers on both sides: 236 on the left, 102 + 131, or 233, on the right. So there must be 3 additional particles (neutrons) on the right.