I have a big exam coming up in January and a small portion of it is on Delay calculations. My tutors are not very helpful when it comes to this so I was wondering if I could get some help with[enter image description here][1] understanding the maths (I do not have a strong mathematical background).
[1] Here is the question w/ answers: https://i.stack.imgur.com/7kjWK.png
The packet is placed on the transmission line twice, once by each host (remember, it's store-and-forward). Each time it takes $L/R$ seconds. ($L-$bit packet, host is $R$ bits per second.) As to the $2m$ meters, it's given in the first part of the problem that both $a$ and $b$ are equal to $m$.