HW 7 - Questions 5/6

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?