Answer: 30 feet==========================================================It might help to draw a triangle to represent what's going on. See the diagram below.Let's call the triangle ABC. We'll place point A at the 90 degree angle, so it's at the base of the tower. Place point B where the knight is located. Point C is the location of the window in the tower.The knight is 15 feet away from the base, meaning AB = 15. With respect to the reference angle (B = 60), side AB = 15 is the adjacent side. The length of the ladder BC is the unknown hypotenuse. We'll call this x for now.We'll use the cosine rule to connect the adjacent and hypotenuse.cos(angle) = adjacent/hypotenusecos(B) = AB/BCcos(60) = 15/xx*cos(60) = 15x = 15/cos(60)x = 30Your calculator needs to be in degree mode. Because x = 30, we conclude that the ladder needs to be BC = 30 feet long.Side note: For any special 30-60-90 right triangle, the hypotenuse is always twice as long compared to the shorter leg.