On selling 9 balls at Rs. 720, there is a loss equal to the cost price of 5 balls. The cost price of a ball is:  Choose the correct choice from the following options.
A) s . 145  B) s . 150  C) s . 155  D) s . 160  E) s . 180

Rationale: "( c . p . of 9 balls ) - ( s . p . of 9 balls ) = ( c . p . of 5 balls ) c . p . of 4 balls = s . p . of 9 balls = rs . 720 . c . p . of 1 ball = rs . 720 / 4 = rs . 180 . answer : option e"
Answer: E