initial capacity of token bucket is given as =$10^{7}$ bits
in every 10 $\mu$ sec => 1 token is added
in 10*$10^{-6}$ sec => 1 token is added
in 1 sec =>$10^{5}$ token added
token rate=$10^{5}$ tokens/sec.
1 token is equivalent to 16 (2*8) bits of data
due to token rate we are able to send 16*$10^{5}$ bits/sec from the host.
suppose the host transmit at maximum rate (i.e. 8mbps) for t secs
total data sent by host in t secs= 8*$10^{6}$*t
this data must be equal to the original capacity of token bucket + data transferred in 't' time due to token rate
8*$10^{6}$*t = $10^{7}$ bits + 16*$10^{5}$*t
t=1.5625s