The distance d, in meters, that a rhinoceros runs in s seconds is represented by the equation d=16s. What is the constant of proportionality (unit rate) of d to s?

time          Distance                Distance / Time
2hrs          90 miles                  90 miles / 2 hrs =  45 miles / hr
3hrs          135 miles                135 miles / 3 hrs =  45 miles / hr
5hrs          225 miles                 225 miles / 5 hrs =  45 miles / hr
6hrs          270 miles                  270 miles / 6 hrs =  45 miles / hr

Constant of proportionality is 45 miles / hr. This is the same for the four values. The unit rate is also 45 miles / hr.

Let us assume the Distance , d is directly proportional to Time, t
d α t
d = kt 
Constant of proportionality is k which is D/T
d = 45t