A ship travels from a point near Hawaii at 20° N latitude directly north to a point near Alaska at 56° N latitude.

a) Assuming the Earth to be a sphere of radius 4000 mi, find the actual distance traveled by te ship.

b) What fraction of the Earth's circumference did the ship travel?

I have no idea how or where to start on this problem. Can anyone help me? I read on this site that the degrees of a spherical triangle add up to more than 180°.. so I dunno how to begin the problem..

KryssTal : Spherical Trigonometry
The site also sows cosine and sine rules for spherical trig, but I don't see how I could use those since they don't give me much values in the problem to start with.

Help please?