1. The problem statement, all variables and given/known data The river flows 5km/hr in the west direction. The boat that has a speed of 10km/hr. It starts from the south bank to the north. Then the question is to essentially find the angle theta. 2. Relevant equations Tan-1(5/10) or Tan-1(10/5) 3. The attempt at a solution Tan^-1(5/10) or Tan^-1(5/10). So basically the answer is asking to find the angle theta, when drawing the triangle I get this. Now basically I'm confused on what angle to take. If I take the top left angle then I would get tan^-1(10/5) but, if I take the bottom right get tan^-1(5/10). All the answers provided are in terms of "east of north". If I look at this logically, north east is the top right but the east of north would be the angle at the bottom right. I'm just trying to know which one would be correct.