A table can be used to find the rate of change by giving you a visual representation of how the operation changes over time for example in the link i'm about to post you can see how much more money is earned as more cars are washed, it is showing how much money is being made OVER TIME, hope this helps :)
now to answer your second question, say you would like to know how many miles Tracy ran over a course of 2 hours, the x axis would be the miles and the y axis would be the time, then you would plot the different points on the graph showing the rate at which she is running
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to answer your last question a linear interval would be a sequence of numbers that when places on a number line they will form a line, a nonlinear interval is a sequence of numbers that don't make a line because there are inequities meaning the numbers in the sequence are all over the place
Hope this helps and i will post the pictures so you can have a visual representaion
