The situation described in the problem can be seen in the following diagram:
The direct line distance from the plane to the runway is the hypotenuse of the right triangle in the diagram. From the triangle we have:
[tex]\begin{gathered} \cos 10=\frac{6}{d} \\ d=\frac{6}{\cos 10} \\ d=6.09 \end{gathered}[/tex]Therefore the direct line distance is 6.09 km (rounded to two decimal places)
