Hello,

I've attached a diagram as you requested.

Let d be the distance between the 2 boats.

Let t be the time the boats traveled since the powerboat passed the buoy.

Use Pythagorian rule:

. Expand the brackets and collect equal powers:

. d² has a minimum if d has a minimum. Thus it is sufficient if you calculate the minimum of d² = D

. D'(t) = 0 if

That means after 7/25 hours = 16 min 48 s, the distance is a minimum. Plugin this value for tand calculate d.

d = 24 km

EB