Finding molecular mass and moles

Question

Assignment:

First, how many moles are present in each of the following masses? 2.58g of SrSO₄ and 2.53 x10^-3g of Ag₂CO₃.

Second, going in reverse, How many grams are necessary to obtain the given number of moles? 3.20 x 10^-4 moles of NaOH and 6.42 moles of AgNO₃.

Provide complete and step by step solution for the question and show calculations and use formulas.