Help with a P controller for a plant with delay

[betovm]

Hi I have to do a P controller with a plant with a delay (exponential in the transfer function). It need to have a margin phase of 40 degrees and I have to find wu in order to calculate de C0 coefficient for the P controller. Given that there is an exponential in the transfer function I can't calculate wu. I am posting the original problem but it is in French. If someone knows how to do it or has any clue it will be very helpful, thanks!