Explanation:
There may be an easier way, but here is what I would do:
Convert positions to cartesian coordinate points, then
Use distance formula to find how far apart the points are
Boat B
x = 4.5 cos 48 = 3.011 y = 4.5 sin 48 = 3.344
Boat C
x = 3.3 cos 148 = -2.799 y = 3.3 sin 148 = 1.749
Now use distance formula
d^2 = ( 3.011 - - 2.799)^2 + ( 3.344 - 1.749)^2
d = 6.0 km apart