Answer:
l/R1 + l/R2
Explanation:
Assuming the length of the packet = l
The transmission rate between sending host and switch = R1
The transmission rate between the switch and the receiving host = R2
The store and forward packet-switching stores packets and validates them before transmitting them to the receiving host. So the end-to-end delay L is the sum of the transmission delay from the sending host to the switch and the switch to the receiving host, that is;
L = l/R1 + l/R2