D.
By looking at the scatterplot, we can identify the ‘trend’, or the general outline of the dots and where they’ll be. Using this, we can predict where a given dot will be in the sequence.
Since the dot for 3 chapters is at 80(roughly) and the dot for 5 chapters is at 140(at the lowest), we can infer that the dot for four chapters will be somewhere in the range of 81-139. From there, we can rule out 140 and 150 as answers, and we can use an inference to pick 120 as the answer.
Hope this helps! :)
