Null and Alternative Hypotheses · Exercise 8

Suppose that a recent article stated that the mean time spent in jail by a first–time convicted burglar is 2.5 years. A study was then done to see if the mean time has increased in the new century. A random sample of 26 first-time convicted burglars in a recent year was picked. The mean length of time in jail from the survey was 3 years with a standard deviation of 1.8 years. Suppose that it is somehow known that the population standard deviation is 1.5. If you were conducting a hypothesis test to determine if the mean length of jail time has increased, what would the null and alternative hypotheses be? The distribution of the population is normal.
(a) H_0: ________
(b) H_a: ________

Its source prints no answer for this problem, so there's nothing to check against.

OpenStax, Introductory Statistics 2e · §9.1 Null and Alternative Hypotheses · Exercise 8