#### Answer

a) $\frac{dP}{dt}$ represents the percentage rate of change per year.
b) $\frac{dP}{dt}|_{t=2}$ represents the percentage rate of change in the city's electrical power after 2 years.

#### Work Step by Step

a) $\frac{dP}{dt}$ represents the percentage rate of change in the city's electricity power that is produced by solar panels since 2000.
b) $\frac{dP}{dt}|_{t=2} = 3.5$ represents the percentage rate of change of the city's electrical power produced by solar panels in the year 2002.