A continual management problem is that the executive stak...

A continual management problem is that the executive stakeholders, i.e. the clients, as well as user stakeholders frequently need to know how long the project will take and how much it will cost. How does the project manager answer that question? How does he/she give a meaningful answer but also recognizing that it may be completely erroneous? How does he/she protect himself, yet give an answer to help executive management make a decision whether to invest in the new system or not?