I need help with this problem, so far i onli be capable to calculate de O2 and N2 weights.

A mineral of a process contains contains 90% FeS2 and 10% inerts by weight. This material it is calcined with 25% excess air, according to the reaction:

FeS2 + 02 ► Fe203 + S02

The solid mixture leaves the calciner with 13% inerts by weight and the rest FeS2 and Fe203

a) Calculate the weight of solids leaving the calciner.

b) Determine the% conversion based on FeS2 •

c) Calculate the Orsat analysis of the gases produced.