Host A transmits a packet to Host B via host C, and the probability that a packet is received correcly from A to B is P,(thus (1-P) for not correctly).
If It's not sent correctly, then resend it. And it takes L time to send a pacekt from A to B.

So, it follows a geometric distribution that A has to send the packet k times, before it's sent correctly

ie, P(1-P)^(k-1)

Similarly, the same rule applies to the transmission from B to C, except the packet is only sent once from B to C, and if a packet is not sent correctly to C from B, then you have to go back to A, and repeat the process.

So, it asks to find the expected length of time it takes for B to receive a correct packgee from A via c

so, how would I do it?