Suppose, a lighthouse operator (L) observes a fishing boat (B) that is moving straight away from the light house. The level of the lighthouse operator is 20 m above the level of the sea. At a particular instant, the lighthouse operator observe the boat (B1) with a depression angle of 800 . Two minutes later, the boat (B2) was observed with a depression angle of 400 . What is vB, the speed of the boat as measured by the light house operator in m/s