They meet every 24 seconds, which means they can run a lap together every 24 seconds.

A runs a lap for 40 seconds, so in 24 seconds, he can run 24/40=0.6 lap, which means that the remaining 0.4 lap is completed by B in 24 seconds, so it takes B 24 seconds to run 0.4 lap and 24/0.4=60 seconds to run a lap.

Now they are walking in the same direction. If they want to meet, it must be an integer circle in which A just exceeds B, that is, one, two or three laps, and so on. ...

A runs 1/40 laps per second and B runs 1/60 laps per second, so A runs1/40-1/60 =1120 laps more than B, so it needs 65438 laps.