I recently applied to a job and took a programming test. I didn't hear back, so I'm assuming I didn't get the position. I was able to answer all of the questions except one. I'm trying to find out what the answer is because its been bugging me, but I'm not having any luck. The question is a math calculation.

A man is standing in the middle of a long dry riverbed when he sees a wall of water heading towards him. If the water is moving at 8 times the speed at which the man can run, then he’ll have the best chance of escape by running:

A) Straight toward a river bank
B) Toward a bank, but at a slight angle away from the water
C) Away from the water, but at a slight angle toward the bank

Give a short explanation of your reasoning. Establish your answer mathematically.

Does anybody know what exactly needs to be done to find the optimal path? Is there an exact equation to use?

Thanks for any help you can offer.