The time between visits to a U.S. emergency room for a member of the general population follows an exponential distribution with a mean of 2.5 years. what proportion of the population

The time between visits to a U.S. emergency room for a member of the general population follows an exponential distribution with a mean of 2.5 years. what proportion of the population
a. will visit an emergency room within the next 6 months?
b. will not visit the ER over the next 6 years?
c. will visit an ER next year, but not this year?
d. find the 1st and 3rd quartiles of this distribution