Silvia:
ListPlot can handle several different shapes of data.
When you pass in a list of list of numbers, ListPlot assumes that you want to plot 3 variables. Since you passed a list of numbers for each of those variables, ListPlot assumes you provided the y values and it assumes the x values, starting at one and counting up. That is why you have three x values (1, 2 and 3).
If you instead pass in a list of list of points, you will get what you are looking for. That would look something like:
ListPlot[{{{24, 5}, {72, 10}, {168, 8}}, {{24, 15}, {72, 32}, {168, 10}}, {{24, 25}, {72, 64}, {168, 15}}]
The documentation explains this a bit better, but it takes a while to get used to the Wolfram documentation style.
Good luck and have a great and safe rest of your week.
