The first drop is 210 metres. After this the ball will rise by 175 metres and fall by 175 metres which is 5/6 th of 210 .

This process will continue in the form of infinite GP with common ratio 5/6 and first term 175.

The required answer is given by the formula: a/(1-r)

that is 175/(1 - 5/6) = 1050 metres.

Hence, 1050 metres is the answer.