Aship is 50 miles west and 31 miles south of a harbor what bearing should the captain use to sail directly into the harbor?

31.8 degrees north of east (not sure what format the question wants)

To get this answer you draw a triangle with the line between the ship and the harbor, a line going horizontally, from the ship and ending below the harbor, and a line going vertically down from the harbor to the end of the horizontal line. The horizontal line has a length of 50 and the vertical line has a length of 31. Using inverse tangent, you can find the angle between the ship and the harbor, which is

arctan(opposite/adjacent) opposite being the vertical line, and adjacent being the horizontal line

arctan(31/50) (or tan^-1(31/50))
which gets you 31.8 degrees

a. i. only is correct.