The information given in the question can be represented by the three sides if a right angled triangle.
Let the direct line from the airplane to the start of the runway be represented by x. So that applying the appropriate trigonometric function, we have;
Cos θ =
Cos =
0.9903 =
⇒ x =
= 6.0588
x = 6.06 km
The direct line from the airplane to the stat of the runway is 6.06 km.