Lattice enthalpy A2 chem question!

Chemistry question I'm struggling with... I feel like I'm almost there but I'm not getting the right answer, I would really appreciate some help!

The molar enthalpy change on decomposition of calcium carbonate into calcium oxide and carbon dioxide is 178kJmol-1.
Given the lattice enthalpies of CaCO3 (-2799kJmol-1) and CaO (-3396kJmol-1) find the enthalpy change when bonding an oxide ion to carbon dioxide in the gas phase.

Any clues or explanations method wise would literally be amazing tysm

I do not have the answer and I am struggling with this too. You got any ideas?

This is an old thread, so really you should have started your own.

What have you tried so far?

I just don't know where to start. I tried 178=-2799-3396+____ because it felt right but it's not. I'm probably missing a big point here.

Have you thought about drawing a Hess cycle?

Have you thought about drawing a Hess cycle?

Oh wait so I used my logic to do the calculation at first and then used the hess cycle as you suggested and got the same answer but different sign. Wow. I got it now, thank you and have a nice evening!