How to solve this :calculate file size problem

Question

An audio recording has the following settings:- sampling rate 16000 samples per second- 32 bits per sample.

An audio file size after the recording is 4 kilobytes. How long is the audio recording (in msec)?

Note: 220 = 1 mega

Answer 1

16000 samples / sec * 32 bit / sample = 512000 bits / 8 = 64000 bytes/sec

filesize is 4kb = 1024*4 = 4096 bytes

so length is 4096 bytes / (64000 bytes/sec) = 0.064 sec = 64 msec