Answer: So you may know that that the time for downloading a file of Amb is B seconds, where A and B are numbers.
then if some file weights C, that is 10 times more than A, and you assume that the download speed sees this has downloading 10 times the Amb file The time for downloading this second file will be 10*B seconds.
This is an example of a linear relationship between the size of a file and the time to download the file.