Provide your best answer for the following math problem. Give ONLY the answer, no other words or explanation.
For example:

Answer: <most likely answer, as short as possible; not a complete sentence, just the answer!>.

The problem is: a runs twice as fast as b and gives b a start of 83 m . how long should the racecourse be so that a and b might reach in the same time ?
none of the above
Let x be the length of the racecourse. Then the time it takes for a to run x is x/2a, and the time it