Answer: 5 km.

Solution: a similar solution to this problem is present in option 1 under the same number.
4. From the town "U ${ }^{\prime}$ " to the town " $A x$ ", Ivan set off on his bicycle at $11^{00}$ AM, having traveled two fifths of the distance, he passed the town " $O x$ ", from which at that moment Peter set off on foot towards the town "Ux". At the moment when Ivan arrived in the town " $A x$ ", from there in the opposite direction Nikolai set off on his bicycle and arrived in the town "Ux" at $12^{00}$ of the same day. How many kilometers from the town " $A x$ " did Nikolai catch up with Peter, if Peter arrived in the town "U $\$ " at $13^{30}$ of the same day, while the speed of each participant was constant, and the distance between the towns "U" and " $A x$ " is

7 km.

( 7 points)