A boat sails on a bearing of N15°E for 10 km and then on a bearing of S85°E until it is due east of the starting point. What is the distance from the starting point to the nearest kilometre?

3 answers

So, I got:
b/sin(85) = 10/sin(5)
b = 10sin(85)/sin(5)
b = 114.3km

Answer is 113 km
Can anyone tell me what I have done wrong? Thank you.
Your symbols lead to confusion. They are both incredibly archaic methods of direction notation. All modern navigation systems use north as a reference and measure degrees CW from that reference.
I can tell from your numbers you did not draw the vectors head to tail, and figure the angle between them correctly.
As bobpursley noted, you did not calculate the angles correctly.
you have to add 85+15 for the top angle.
My diagram has angles of 75, 100, and 5 degrees, and I get
b/sin100 = 10/sin5
b = 112.994.. or appr 113