how to calculate end-to-end delay in this scenario
<p>Here is my question:
We wish to send a message of size 150,000 bytes over the network. There are four hops, each of length 20km and running at 100 Mb/s. However, before sending we split the message into 1500 byte packets. What is the end-to-end delay of the message? Use speed of light in copper = c = 2 * 10^8 m/s, and round your answer to the nearest integer millisecond.</p>

<p>What I have so far is 48ms, which I calculated in the following fashion:
    1500 bytes = 12,000 bits
    12,000 bits/(100x10^6)[100Mb/s] = 0.00012s
    20km/(2*10^8)[speed of light in this equation] = 1e-7
Add them up and you get 0.0001201s per hop x 4 hops = 0.0004804s -> 48ms rounded to nearest integer. </p>

<p>Apparently this is not correct and I cannot figure out my error. My online course has no assistance available so I'm turning to SO. If anyone can point me in the right direct, I would appreciate the help.</p>