Hardest Math Topic So Far

For me the hardest Math topic so far, or at least one I didn't quite understand was the d= r x t (distance is equal to rate times time.) I don't know why but I didn't understand, and I didn't understand when we needed to put it in a chart and then do an equation with it. When I studied it, there were times I knew how to do it, and do the chart and then the equation but it was complicated for me, I don't know how to do it now. Well, this is the only topic I don't understand of the ones we have studied, there have been ones that I don't understand in the beginning, but I always learn it after.