3. Before the trial run of one of the units of the hydropower station under construction, it was found that a fishing net is located $S$ km upstream from the dam. The river current speed is $v$ km/h. The hydropower station workers decided to go there by boat. Removing the net will take 5 minutes. What should be the boat's own speed so that the entire trip (including the time required to remove the net) takes no more than 45 minutes?
Answer. $x \geqslant \frac{3 S+\sqrt{9 S^{2}+4 v^{2}}}{2}$.
Criteria. «+.» Answer $x=\ldots$ instead of $x \geqslant \ldots ;$ «士» answer found in different units of measurement; «干» in the correct solution, the comparison of the roots of the quadratic equation with zero was not performed, leading to an additional piece of the solution $\left(0 ; \frac{3 S-\sqrt{9 S^{2}+4 v^{2}}}{2}\right)$.