Since the creation of a social program, the percent of persons 65 years and over with a family income below the poverty level has declined.  The percent can be approximated by the function P(t)=30.71-5.77ln t, where t is the number of years since 1965.  

Find the percent of persons 65 & over with family income below the poverty level and the rate of change in 1970.

i know how to find the percent, but don't know how to find the rate of change.  Please help!