So the store bought 9 cases of lightbulbs and in a case, there are 48.
9 * 48 = the number of lightbulbs in the nine cases. 432 is the number of light bulbs in the 9 cases they bought in May. So then let's move on to the cases they bought in June. Do the same thing 8 * 48 is 384. So then add the two amounts together and then you will get 816 which will be your answer. I hope this helps!