To find the unit rate of the cost of the paper towels in dollars per roll, you need to divide the total cost by the number of rolls.
Given the equation: \[ c = 1.29r \]
The unit rate can be found by isolating the cost per roll, which is expressed as: \[ \text{Cost per roll} = \frac{c}{r} \]
Substituting the equation for cost: \[ \text{Cost per roll} = \frac{1.29r}{r} \]
When you simplify that, the \( r \) cancels out: \[ \text{Cost per roll} = 1.29 \]
Thus, the unit rate of the cost of the paper towels is \( 1.29 \) dollars per roll.
So the answer is: \[ 1.29 \]