Question 937343
distance tanker had already traveled when the cruise ship sails:
s = d/t
d = st
d = 10*2
d = 20 nm
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relative speed of the two ships:
s = 10 + 18
s = 28 kts
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time after cruise ship sails, when the two ships are 209 nm apart ...
the two ships are already 20 nm apart when cruise ship sails: 
d = 209 - 20
d = 189
t = d/s
t = 189/28
t = 6.75 hr
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