Port A is defined to be the origin of a set of coordinate axes and port B is located at the point $(70, 30)$, where distances are measured in kilometres. A ship $S\_1$ sails from port A at 10:00 in a straight line such that its position $t$ hours after 10:00 is given by $r=t(10, 20)$ (I don't know how to make column vectors sorry, but that 20 should be under the 10)

A speedboat S2 is capable of three times the speed of S1 and is to meet S1 by travelling the shortest possible distance. What is the latest time that S2 can leave port B?

My working so far:

$r\_1=t(10, 20)$

$r\_2=(70, 30)+(t-k)(x, y)$ as the second ship sets of k minutes later. How do I know what the direction vectors x and y are though? Maybe I'm not visualising the problem correctly...