China's push to install more wind energy capacity has started paying off. As of 2012 , wind energy had become the country's third largest source of energy, after coal and hydroelectric power. The amount of wind energy generated in China from 2005 through 2012 grew at the rate of
$$r(t)=5.018 t-3.204 \quad(0 \leq t \leq 7)$$
terawatt-hours/year, in year $t,$ where $t=0$ corresponds to $2005 .$ The amount of wind energy generated in 2005 stood at 1.8 terawatt-hours.
a. Find an expression giving the amount of wind energy generated in year $t$
b. How much wind energy was generated in $2012 ?$
c. If the trend continued into 2013 , how much wind energy was generated in China in that year?