Модуль: Information encoding: text, graphics, sound. Problem solving

Задача

The music piece has been digitized and recorded as a file without the use of data compression. The resulting file was transmitted to city A via a communication channel. Then the same musical fragment was re-digitized with a resolution 2 times higher and a sampling rate 3 times lower than the first time. Data compression was not performed. The resulting file was transferred to city B in 15 seconds. The throughput of the communication channel with city B is 4 times higher than the communication channel with city A. How many seconds did it take to transfer the file to city A? 

Write down only an integer in your answer, you do not need to write a unit of measure.