Fe                ----->  Fe⁺⁺  + 2e-         

so E for the new reaction = [1F(0.77) + 3F(0.04)]/2F = 0.89/2 = 0.445

so it will be -0.445 for the reverse, you are asking for reduction and i submitted the answer for oxidation so the duality created.

according to the given reaction we get 2L monooxide by 1L dioxide,

initially litres of CO₂  = x so it will form 2x litres of CO

and 1-x litres CO are present from the start so total litres of CO = 2x+1-x = 1+x