I don't know if you can find a rate with 2 numbers. You can find a rate with 2 sets of numbers. If you only have 2 numbers you cannot do much.
however if the problem says something like x changed from 45 to 65 over some x values that are not given you can find the rate. this is because you are actually given 2 sets of numbers. It it doesn't have to be x and y. It could say it another way. let's say it says you get on the freeway at 45 mph and when you see yout exit sign you are traveling 65 mph. What is your rate of change. this can actually be written in (x,y) form. in both of these examples you can say (x1, 45) and (x2, 65).
well the rate of change would just be the difference in y values per the difference in x values. If you think about it, this is just the slope of the line it creates. (y2 - y1) / (x2 - x1). or: (64 - 45) / (x2 - x1). 20 / (x2 - x1).
this can be worded as we had a rate of change of 20 per (x2 - x1) time period.
or you could say out rate of change was just 20 if of the time period is already understood.
i hope this helps. I am not sure if it was what you were asking
