97. There is a river between Reservoir A and Town B. When the reservoir does not release water, the water in the river does not flow; when the reservoir releases water, the water in the river flows at a uniform speed. When the reservoir is not releasing water, Speedboat M departs from A towards B and travels for 50 minutes, covering $\frac{1}{3}$ of the river's length. At this point, the reservoir starts to release water, and the speedboat travels another $\frac{1}{3}$ of the river's length in just 20 minutes. At this point, the driver turns off the speedboat's engine and lets the speedboat drift with the river's current, and it takes $\qquad$ minutes for the speedboat to reach B.
Answer: $\frac{100}{3}$