1. **State the problem:** We need to write an equation for the cost $y$ to rent a kayak, which is proportional to the number of hours $x$ rented. 2. **Understand the proportionality:** If $y$ is proportional to $x$, then $y = kx$ where $k$ is the constant of proportionality. 3. **Use the given information:** It costs 27 dollars for 3 hours, so substitute $y=27$ and $x=3$ into the equation: $$27 = k \times 3$$ 4. **Solve for $k$:** $$k = \frac{27}{3} = 9$$ 5. **Write the final equation:** $$y = 9x$$ This means the cost is 9 dollars per hour of kayak rental.