1103021903

An observer was watching an approaching plane flying at a height of $3000\mathrm{m}$ in a straight line with constant velocity. At the first moment of measurement the observer saw the plane to be at an angle of elevation of ${25}^{\circ }$. After $10$ seconds the angle of elevation changed to ${35}^{\circ }$. What was the speed of the plane? Round the result to ones.