Balancing using half reaction method

[a.a]

Homework Statement

The redox reaction below occurs in basic solution. Balance it with the smallest whole number coefficients and determine the coefficient for OH-.

H2CO(g) + Ag+(aq) ---> HCOOH(aq) + Ag(s).

Homework Equations

The Attempt at a Solution

I got the oxidation numbers and found that Ag is reduced and the H2CO is oxidized, but I can't balance the half reactions, this is what I came up with:

Ag+ + 1e- ---> Ag

H2CO + H2O ---> 2HCOOH + 1e- + H2O
Any help?

 

[a.a]

sorri i think i got it, can someone check?:

2OH- + H2CO ---> 2HCOOH + 1e- + H2O

so the coefficient for OH- is 2?

 

[Borek]

Charge is not balanced, carbon is not balanced, oxygen is not balanced... haven't checked hydrogen.