Question

Can you check these? And I need help on one.
Oxidation Number Method of Balancing Redox Reactions
1)Neutral Solution
Sn^2+ + Fe^3+ ----> Fe^2+ + Sn^4+
Balanced equation
Sn^2+ + 2Fe^3+ ----> 2Fe^2+ + Sn^4+

2)Acidic Solution
Fe^2+ + Cr2O7^2- ---> Cr^3+ + Fe^3+
Balanced equation
14H^+ + 6Fe^2+ + Cr2O7^2- ---> 2Cr^3+ + 6Fe^3+ + 7H2O

3) Basic Solution
Mno4^- + SO3^2- ---> SO4^2- + MnO2
Balanced Equation
I can't figure out how to do this one.
First -
2MnO4 + 3So3^2- ---> 3SO4^2- + 2MnO2
Then I added H2O on one side to help balance the O's. Then I had to add an H+ to the reactants side to balance out the H's. Since it was a basic solution I had to add OH- to the answer side. But then I had to add it to the other one as well.
I have -
OH- + H- + 2MnO4 + 3So3^2- ---> 3SO4^2- + 2MnO2 + H2O + OH-
OH- + H- becomes H2O...the H's are unbalanced and I don't know how to keep them balanced while making sure it's basic.

4) Basic Solution
CH3OH + MnO4^- ---> MnO4^2- + CO3^2-
Balanced Equation
CH3OH + 6MnO4^- ---> 6MnO4^2- + CO3^2-

I don't know how to balance out the H's.

Also, can you please explain to me the half reaction method?
Can you do this question and explain what you did.

Hg + H3IO6^2- ---> Hg2O + IO3^-

Thanks so much for all the help!