The national health expenditures are projected to grow at the rate of
$$
r(t)=0.0058 t+0.159 \quad(0 \leq t \leq 13)
$$
trillion dollars/year from 2002 through $2015 .$ Here, $t=0$ corresponds to 2002. The expenditure in 2002 was $$\$ 1.60$$ trillion.
a. Find a function $f$ giving the projected national health expenditures in year $t$.
b. What does your model project the national health expenditure to be in 2015 ?