Based on data obtained by polling automobile buyers, the number of subscribers of satellite radios is expected to grow at the rate of
$$
r(t)=-0.375 t^{2}+2.1 t+2.45 \quad(0 \leq t \leq 5)
$$
million subscribers/year between $2003(t=0)$ and 2008 $(t=5)$. The number of satellite radio subscribers at the beginning of 2003 was $1.5$ million.
a. Find an expression giving the number of satellite radio subscribers in year $t(0 \leq t \leq 5)$.
b. Based on this model, what was the number of satellite radio subscribers in 2008 ?