Hal gives roping lessons at the Sundown Corral. A 3.5-hour lesson costs $105.00. The cost of a lesson is proportional to the duration, in hours, of the lesson. What is the constant of proportionality in terms of dollars per hour?
The constant of proportionality is the unit rate that relates the cost of the lesson to the duration of the lesson.
In this case, the cost of a 3.5-hour lesson is $105.00.
To find the cost per hour, we divide $105.00 by 3.5: $$\frac{105}{3.5} = \boxed{30}$$
Therefore, the constant of proportionality is $30 per hour.