3. (3 points) Chester needs to travel from Hualien to Lukang, Changhua, to participate in the Hua Luogeng Mathematics Competition. Before setting off, his father checked the car's odometer, which showed a palindrome number 69696 km (Palindrome number: a number that reads the same backward as forward). After driving for 5 hours, they arrived at their destination, and the odometer showed another palindrome number. During the journey, the father never exceeded a speed of 85 km/h. What is the maximum possible average speed of the father's car in km/h?
【Analysis】To maximize the average speed, the other palindrome number also needs to be maximized. Since $69696+85 \times 5=70121$, and the largest palindrome number less than 70121 is 70107, the maximum average speed is $(70107-69696) \div 5=82.2$ (km).

【Solution】Solution: $69696+85 \times 5=70121$ (km)
The largest palindrome number less than 70121 is 70107,
$$
\begin{aligned}
& (70107-69696) \div 5 \\
= & 411 \div 5 \\
= & 82.2(\mathrm{~km})
\end{aligned}
$$

Answer: The maximum average speed of Dad's driving is 82.2 kilometers per hour.
Therefore, the answer is: 82.2.