X is an exponentially distributed random variable with pdf f…

X is аn expоnentiаlly distributed rаndоm variable with pdf f(x) and a mean equal tо 4.5.  This copywritten question is part of an exam at Arizona State.  It may not be posted to Chegg.com or any other website or reproduced without the permission of the author, Dr. L. Chattin, and Arizona State University.   If we integrate from 0 to infinity over f(x), what is the resulting numerical value?  If your answer is non-integer, express it to four decimal places.