Please help me solve these missing coefficient

How many moles of sulfur dioxide are produced when 4.38 moles of oxygen completely react with iron (iv) sulfide

Aconcentrated solution of ammonia is 14.8m and has a density of 0.899g/l. what is the concentration of ammonia in this solution in weight percent (%w/w)?

Sum of brother and sisters age is 26. four times the brothers age is subtracted from three times the sisters age, the difference is 8. what are the ages of the brother and sister?