Directions (Questions 508 to 509): These questions are based on the following information: 85 children went to an amusement park where they could ride on merry-go-round, roller coaster and Ferris wheel. It was known that 20 of them took all the three rides and 55 of them have taken at least two of the three rides. Each ride costs Re 1, and the total receipt of the amusement park was Rs 145. How many children took exactly one ride? (a) 5      (b) 10      (c) 15     (d) 20