## 90. Math Puzzle 11/72

A reconnaissance boat, which belongs to a fleet, is given the task 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 (1 knot = 1 nautical mile per hour), and the speed of the reconnaissance boat is 28 knots.

After what time can the reconnaissance boat be expected back at the fleet?
$28 x+15 x=140$, i.e. $x=3 \frac{11}{43}$

The scout will return to the fleet formation in approximately 3 hours 15 minutes.