## 120. Math Puzzle $5 / 75$

A reconnaissance boat of the People's Navy, which belongs to a fleet, is ordered to explore a sea area of 70 nautical miles in the direction of the fleet's movement. The speed of the fleet is 15 knots, and the speed of the reconnaissance boat is 28 knots.

After what time can the boat be expected back at the fleet (1 knot = 1 nautical mile per hour)?
Sought time: $x$ hours.

During this time, the fleet covered $15 x$ nautical miles, and the scout covered $28x$ nautical miles. The scout traveled 70 nautical miles in the direction of travel, but on the return trip, only a part of the distance had to be covered, with the remaining part covered by the fleet.

Together, they covered a distance of $28 x + 15 x = 140$ nautical miles, which follows: $x = 3 \frac{11}{43}$.

The scout returns to the fleet in approximately 3 hours and 15 minutes.