(In this question the unit vectors i and j are due east and north respectively.)

At noon a ship S is 600m due north of an observation point O and a speedboat B is 120m due north of the same point. The ship S has a constant velocity of

and the speedboat B has a constant velocity of

.

b). Show that S and B will collide and find the time when this collision occurs and the position vector of the point of collision.

My attempt:

From there I need to find what t equals. That would give me the time when they collide. I've tried rearranging the equation to get t on one side, I've even tried finding the magnitude of the component vectors, where 7i+24j would be 25, but I just can't work it out =\ . Please tell me how to work it out, and I will go from there.