In Q5 we asked to find the exact cost and delay, we assume c(XOR) = c(AND) = c(NOT) = 1 ?

same for delay?.

And c(IN/OUT) = 0, same for delay?

This is a simplifying assumption justified as follows.

In any case, the cost (or delay) of a simple gate is constant. If we do not care about constants, then we might as well set it to zero.

Inputs and outputs are a fixed part of the circuit, so why charge for it?