days, $($b$)3$ days, and $($c$)6\mathrm{.}5$ days. $($d$)$ Are the slopes of the tangent lines to $C$ always positive or always negative? What does this indicate about the rate of change of the mineral level?

$($a$)$ The rate of change of the mineral level with respect to time for $0$ days is $-0\mathrm{.}29$ milligrams per cubic centimeter per day. $($Round to two decimal places as needed.$)$

Interpret the rate of change when $t=0.$

At $0$ days, the mineral level in the bloodstream is decreasing by $0\mathrm{.}29m\frac{g}{c}{m}^3$ per day.

$($Type integers or decimals rounded to two decimal places as needed.$)$

$($b$)$ The rate of change of the mineral level with respect to time for $3$ days is $$ milligrams per cubic centimeter per day.

$($Round to two decimal places as needed.$)$