For part b of this question, both of the process Omega and Zeta have higher IRR and MIRR than cost of capital of 13%. So both of them should be accepted.
So why the answer says ‘process Zeta should be adopted as a result…’?
But they cannot accept them both – the first paragraph of the question makes it clear that they have to choose one or the other (or, obviously, neither of them 🙂 )