A Cepheid variable star is a star whose brightness alternately increases and decreases. Suppose that Cephei Joe is a star for which the interval between times of maximum brightness is 6.6 days. Its average brightness is 2.6 and the brightness changes by /-0.6. Using this data, we can construct a mathematical model for the brightness of Cephei Joe at time t, where t is measured in days:

(a) Find the rate of change of the brightness after t days.
(b) Find the rate of increase after one day.