Answer
a) the slope is $0.0417D=8.34$, the average increase in the dosage of the drug per year in age.
b) $8.34$ mg
Work Step by Step
a) We have
$c=0.0417D(a+1)=0.0417Da+0.0417D$
Here, the slope is
$0.0417D=0.0417(200)=8.34$
and it represents the average increase in the dosage of the drug per year in age.
b) Plugging in $D=200,a=0$ we get:
$c=0.0417(200)(0+1)=8.34$ mg
