for a digital time division multiplexing system each voice channel has a bit rate of $64kbp5,32$ voice channeis are mulupiexed $,$ each channel is encoded using $10$ bit pem code. the system uses a single bit for timing at the end of each frame, the bit interval is :

select onit:

a: $0\mathrm{.}647$ miaro second

b$.0\mathrm{.}7gng$ micro sectond

is$.x2\mathrm{.}5$ micre sectang

$18125$ micro sechan