Given the task definition, example input & output, solve the new input case.
The task is to generate the correct answer for a given math problem.
Example: a multiple choice test consists of 4 questions, and each question has 5 answer choices. in how many r ways can the test be completed if every question is unanswered ?
Output: 625
Total r of 5 * 5 * 5 * 5 = 5 ^ 4 = 625 ways to answer all of them. Therefore, the answer is 625.

New input case for you: Problem: a man sitting in a train which is traveling at 36 kmph observes that a goods train , traveling in opposite direction , takes 10 seconds to pass him . if the goods train is 240 m long , find its speed
Output:
50 kmph