please explain step by step. I do not undestand anything

A. Consider a packet of length L which begins at end system A and travels over three links to a destination end system. These three links are connected by two packet switches. Let di, si, and Ri denote the length, propagation speed, and the transmission rate of link i, for i = 1, 2, 3. The packet switch delays each packet by d proc. Assuming no queuing delays, in terms of di , si , Ri , ( i = 1,2,3), and L, what is the total end-to-end delay for the packet? Suppose now the packet is 1,000 bytes, the propagation speed on all three links is 5.0 108 m/ s, the transmission rates of all three links are 2 Mbps, the packet switch processing delay is 3 msec, the length of the first link is 5,000 km, the length of the second link is 4,000 km, and the length of the last link is 1,000 km. For these values, what is the end- to- end delay?

the final asnwer is 38 ms