Sayan is planning to go to a party in durham. if sayan is s minutes early for the party, he incurs cost 5s, and if he is s minutes late, then he incurs the cost 4s. suppose that the travel time from sayan’s home to the location of the party is a continuous random variable having probability density function f(x) = e −x , 0 < x < [infinity] (this is called the exponential distribution). determine the time at which you should depart if you want to minimize your expected cost