Given :
A boat is being pulled into a dock with a rope attached to the boat at water level. When the boat is 12 feet from the dock, the length of the rope form the boat to the dock is 3 feet longer than twice the height of the dock above the water.
To Find :
The height of the dock.
Solution :
This will make a right angle triangle as given in link below .
Now , applying Pythagoras theorem :
Now , h = 5 or h = -9 .
Now , height cannot be negative .
So , height of the dock is 5 ft .
Hence , this is the required solution .