A sailboat departs a harbor sailing due east at a constant 4 knots. Simultaneously, a powerboat begins traveling due north from the same point with a velocity given by v(t) = 2t knots, where t is measured in hours. After 3 hours, how fast is the straight-line distance between the two vessels increasing?
a) 7.2 knots
b) 6.3 knots
c) 6.8 knots
d) 4.8 knots