A boy wishes to throw a ball over a flat-roofed school house that stands 12 m wide and 7.5 m high on level ground. Assuming that the ball will leave his hand at a height of 1.5 m above the ground, determine how far from the wall he should take his stand in order to make the ball clear the roof with least effort, that is, with minimum initial velocity.

A boy wishes to throw a ball over a flat-roofed school house that stands 12 m wide and 7.5 m high on level ground. Assuming that the ball will leave his hand at a height of 1.5 m above the ground, determine how far from the wall he should take his stand in order to make the ball clear the roof with least effort, that is, with minimum initial velocity.