On selling 17 balls at Rs. 720, there is a loss equal to the cost price of 5 balls. The cost price of a ball is:

The correct option is A Rs. 60
(C.P. of 17 balls) - (S.P. of 17 balls) = (C.P. of 5 balls)
$\Rightarrow$ C.P. of 12 balls = S.P. of 17 balls = Rs.720.
$\Rightarrow$ C.P. of 1 ball = Rs. $\frac{720}{12}$ = Rs. 60.