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: the cyclist walking at a constant rate of 15 miles per hour is passed by a car traveling in the same direction along the same path at 60 miles per hour . the car stops to wait for the cyclist for 6 minutes after passing her , while the cyclist continues to go at her constant rate , how many minutes must the car wait until the cyclist catches up ?
18
Approximately 21 minutes.