Helium,it has an atomic mass of 4,which means total no. of protons and neutrons,so I think you meant 2 protons and an atomic mass of 4
Yup go this website for more information http://dwb.unl.edu/calculators/activities/BalEqn.html
Pressure is a scientific parameter that allows us to determine the amount of force being exerted per unit area. The increase in the pressure inside a container containing a gas may be brought upon by the decrease in volume, increase in temperature, or merely by additional of more gas molecules.
1) since we are given percentages, we can assume we have 100 grams of the molecule.
55.6 % Cu ----> 55.6 grams Cu
16.4 % Fe------> 16.4 grams Fe
28.0% S--------> 28.0 grams S
2) convert each gram to moles using the molar masses given



3) we divide the smallest value of moles (0.293) to each one.
Cu --> 0.876 / 0.293= 3
Fe---> 0.293 / 0.293= 1
S-----> 0.875 / 0.293= 3
4) let's write the empirical formula
Cu₃FeS₃