I am sure there must be a typo for the answer for this question.
The last option which is 170000 writes/sec.
1.66 bytes/s ~ 1.7 bytes/sec
average cellphones = 10million
so writes/sec for 10million = 1.7 * 10 million = 17 million
but that is not provided as option rather 170k writes/sec
I am not sure if the last option is correct