packet switching is used so each packet will follow its previous packet in pipelining manner except first packet
total number of bits to send =x bits ,Number of hops=k ,bandwidth = b bps ,each packet contains p data bits and h header bits
number of packets =x/p packets
transmission time (TT)=L/B =(p+h)/b
time taken by first packet =1*k*TT seconds
time taken by all other packets =((x/p)-1)*1*TT seconds
so total time taken=1*k*TT+((x/p)-1)*1*TT =(k+((x/p)-1))*(p+h)/b seconds
time taken by source to transmit =(x/p)*(p+h)/b=x(p+h)/pb