Trevor initially has $65. He buys 3 cans of tennis balls at $6 each.
First, calculate the total cost of the tennis balls: \[ 3 \text{ cans} \times 6 \text{ dollars/can} = 18 \text{ dollars} \]
Next, subtract the cost of the tennis balls from Trevor's total amount: \[ 65 \text{ dollars} - 18 \text{ dollars} = 47 \text{ dollars} \]
Now, we see how many sports towels he can buy with the remaining money. Each sports towel costs $8.
Calculate the number of towels he can buy: \[ \frac{47 \text{ dollars}}{8 \text{ dollars/towel}} = 5.875 \]
Since Trevor can only buy whole towels, he can purchase 5 towels.
Therefore, the answer is: 5 towels