Given that activation energy of the forward reaction is 135kJ/mol
For CO + NO2 yields CO2 + NO

I determined the heat of the reaction to be 227.1kJ/mol

I'm not sure of the exact answer to that, but does the problem say 'activation energy' or 'enthalpy' (or something having the same meaning?

Because activation energy and heat of reaction are two different things.

If the reaction produced 135 kJ/mol for the forward path, then it will take 135 kJ/mol of the backward path.