Calculus Help
posted by Kim .
A model for the length of daylight (in hours) in Philadelphia on the tth day of the year is
L(t) = 12 + 2.8 sin[(2π/365)(t − 80)].
Use this model to compare how the number of hours of daylight is increasing in Philadelphia on March 21 and April 21. (Assume there are 365 days in a year. Round your answers to four decimal places.)

3/31: t=90
4/21: t=111
L'(t) = 2.8cos[(2π/365)(t − 80)](2π/365)
now just plug in t=90 and t=111
The answer, of course, will be in hr/day.