How to calculate overall propagation time for circuitry
2 input OR gate with 2 inputs inverted: (OR)12 ns + (NOT)8 ns

NOR: 4ns

These two are parallel, so you ough to take the longest delay into account, so 12 + 8 = 20 ns till signal arrives to AND.

Then you can add AND(14 ns) in series. So the overall delay is 20 + 14 = 34 ns.