R$19.$ Suppose Host A wants to send a large file to Host B$.$ The path from Host A to Host B has three links, of rates $R_1=500kbps,R_2=2Mbps,$ and $R_3=1Mbps.$

a$.$ Assuming no other traffic in the network, what is the throughput for the file transfer?

b$.$ Suppose the file is $4$ million hytes. Dividing the file size by the throughput, roughly how long will it take to transfer the file to Host B$?$

c$.$ Repeat $($a$)$ and $($b$),$ but now with $R_2$ reduced to $100kbps.$