Balancing equation of potassium dichromate

[calcula]

The problem statement, all variables and given/known data[/b]

I need to balance the following redox equation
K2Cr2O7 + H2C2O4 [2H2O] ----> K[Cr(C2O4)2(H2O)2]2H2O + CO2 + H2O

. The attempt at a solution[/b]
so far I have this but im stuck

14H30{+} + Cr2O7{2-} + 3C2O4{2-} --> 2Cr{3+} + 21H2O + 6CO2

[Borek]

What method are you expected to use? Oxidation numbers or half reactions?

If the latter, try to split it into reduction and oxidation half reactions.