We are given
[tex]y=3.75+1.5(x-1)[/tex]
where
y is the cost in dollars
x is distance in dollars
now, we can find derivative
[tex]y'=\frac{d}{dx}\left(3.75+1.5\left(x-1\right)\right)[/tex]
[tex]=\frac{d}{dx}\left(3.75\right)+\frac{d}{dx}\left(1.5\left(x-1\right)\right)[/tex]
[tex]=0+1.5[/tex]
so,
[tex]y'=0+1.5[/tex]
So,
the rate of change of the cost in dollars with respect to the number of miles is 1.5.........Answer