Bobby would have bought 1.21 dollars worth of items from the school store. This because you would line up the problem. In mine, I did 21 on top, 45 in the middle, and 55 on the bottom. And then I added the 1 + 5 + 5 in the right column which equaled 11. This required me to carry the one to the other side and put the other one down in the answer. Then I did 2 + 4 + 5 + 1 = 12. Then you have to add a decimal which makes the most sense to put it in between the 1 and 2. I hope that this is a help and have a great day! If you can please mark this brainliest and contact me if you need more help!