Moles CO = 10.0 g / 28.01 g/mol = 0.357
the ratio between CO and CO2 is 2 : 2 ( or 1 : 1) so we would get 0.357 mole of CO2 ( 100% yield)
mass CO2 = 0.357 mol x 44.0098 g/mol = 15.7 g ( theoretical yield)
% yield = 12.8 x 100 / 15.7 = 81.5
Hope this helps.