I know the formula for the angle, cos theta = the quotient of the dot product of the product of magnitudes but I am not getting the correct answer for this problem

A ship is a (1,0) on a nautical chart with due north being the positive y-axis. The ship spots a rock at position (2,4)

a) what is the vector joining the ship to the rock?

SR=<2-1,4-0> = <1,4>

b) What angle doe the vector make with due north?

I tried using the vector for due north as <0,1> and got the wrong answer

then I used <1,0> then subtracted the value from 90 for the theta in degrees and still was incorrect.