We have to develop an application for a client. The client has requested a quote from us regarding how expensive the development work is going to be, and we have to provide an estimate. The problem is, in Scrum, we can have rough estimates created by the development team, and this estimate may vary. Moreover, the estimate carried out by the client may be different from the one carried out by our team. If we have to bill the client, the estimate should be correct and justify the productivity we are delivering to the client. How should we bill the client if we cannot estimate precisely?