A cylindrical container has a height of 24 inches. Currently, the container is filled with water to a height of 18 inches. A leaky faucet drips into the container, causing the height of the water in the container to increase by 2 inches per hour. The equation below can be used to find t, the number of hours it would take to fill the container.
18 + ?t = 24
What number should be the coefficient of t?