Suppose that annually an average of library patrons want to borrow a book. A patron borrows the book for an average of 1/ years. Suppose we observe that the book is actually borrowed an average of R...

Suppose that annually an average of library patrons want to borrow a book. A patron borrows the book for an average of 1/
years. Suppose we observe that the book is actually borrowed an average of R times per year. Explain how we can estimate
, which is an unobservable quantity. (Hint: Let U be the expected number of times per year a patron wants to borrow the book and the book is out. Note that

R + U.)