Answer: After t=1 hour the distance between the boat and the steamer be 1300 mi.
Explanation:
Given the speed of boat = 1200 mph
the speed of steamer =500 mph
Distance traveled by boat in time "t"=

Distance traveled by steamer in time time "t"=

As boat head south and steamer heads east ∴ they will make a right angle triangle with hypotenuse=shortest distance between them =1300mi(given)
By Pythagoras theorem

⇒t=1 hour
Thus, after t= 1 hour the distance between them be 1300 mi.