The task is to generate the correct answer for a given math problem.

Example Input: Problem: find the cost of fencing around a circular field of diameter 16 m at the rate of rs . 3 a meter ?
Example Output: 150.84

Example Input: Problem: the area of a circular field is 17.56 hectares . find the cost of fencing it at the rate of rs . 7 per metre approximately
Example Output: 10400

Example Input: Problem: two pipes can fill the cistern in 10 hr and 12 hr respectively , while the third empty it in 30 hr . if all pipes are opened simultaneously , then the cistern will be filled in
Example Output:
6.67 hr