average rate of growth is another way of saying slope, so you can use the slope formula, which in this case would yield (11-4)/(3.5-1.2) which is an average rate of 3.04 inches per day. Essentially, the independent variable is days, because it is the days causing growth not the growth causing days. So that means you do the last day minus first day over the final height minus initial height. Hope this helps :)
