Insulation workers who were exposed to asbestos and employed before 1960 experienced an increased likelihood of lung cancer. If a group of insulation workers has a cumulative total of 100,000 years of work experience with their first date of employment t years ago, then the number of lung cancer cases occurring within the group can be modeled using the function 

N(t) = 0.00437t^3.2.

Find the rate of growth of the number of workers with lung cancer in a group as described by the following first dates of employment.

(a) 5 years ago 

(b) 10 years ago