mental ability

Thirty six vehicles are parked in a parking lot in a single row. After the first car, there is one scooter. After
the second car, there are two scooter. After the third car, there are three scooters and so on. Work out the
number of scooters in the second half of the row.
(A) 10 (B) 12 (C) 15 (D) 17