Help with Chemistry?

Question

I tried a lot but couldn't solve these questions, i'd be really glad if u could help me with at least one question among these:
(ATLEAST ONE !!)

1) 20 mL of a solution of mixture of NaOH and Na2CO3 was first titrated with phenophthalein and M/10 HCl. 15 mL of HCl was required for the end point. After this methyl orange was added and 5 mL of same HCl was again required for next end point. Find out amounts of NaOH and Na2CO3 in the mixture.

2) 44.4 g mixture of Ag2CO3 and NaHCO3 on strongly heating gives a certain volume of gases. The volume of gases at STP reduced by 4.48 litres when treated with KOH. The volume is further reduced by 1.12 litres by treatment with alkaline pyrogallol. Find the % composition of Ag2CO3 and NaHCO3 in the mixture.

3) What volume of 0.1M Mn3O4 solution will be required to completely react with 20 mL of 0.01 M solution of Fe3O4 in acidic medium of H2SO4 such that all the Mn3O4 is converted into MnSO4 & Fe3O4 converted to Fe2(so4)3 ??

Answer 1

3) Mn3O4 + 2 Fe3O4 + 6 H2SO4 -> 3 MnSO4 + Fe2(SO4)3 + 6 H2O

Millimoles of Fe3O4 = 20*0.01 = 0.2

So, Millimoles of Mn3O4 = 0.1

Thus vol. of Mn3O4 soln. = 1 ml