Power delay profile and broadband bus
You would need to check this answer against the text since I see no definition of Ts in the question. 

However, on the assumption that by Ts is meant symbol time, he is distinguishing between broadband and narrowband by comparing the symbol time with the delay. This is reasonable : if Ts >> Td, BW(s) &lt;&lt; BW(channel) therefore this is a narrowband channel.

As for the question how did he calculate Ts? Trivially, by defining the datarate as 25kbps. Assuming a 2 level code (on/off, 1 bit per baud) Ts=1/25000, or 40 us.