8. (5 points) A supermarket has an average of 60 people queuing for payment per hour, and each cash register can handle 80 people per hour. On a certain day and at a certain time, only one cash register was working in the supermarket, and after 4 hours of payment, there were no customers queuing. If there had been two cash registers working at that time, then after how many hours of payment would there be no one queuing?
【Solution】Solution: $80 \times 4-4 \times 60=80$ (people), that is, $x$ hours after the payment starts, there is no customer in the queue. According to the problem, we can get the equation:
$$
\begin{aligned}
80 \times 2 \times x & =80+60 x, \\
100 x & =80, \\
x & =0.8,
\end{aligned}
$$

Answer: There will be no queue 0.8 hours after the payment starts. Therefore, the answer is: 0.8.