You have to regroup because you can't subract 4 - 9. 4 turns into a 14 since you borrow from the left number, 8. 8 turns into a 7 after that. Now, you have to subtract 14 - 9 and 7 - 2. You're answer is 5.5. You can check your work by doing inverse opperations: By adding: 5.5 + 2.9 = 8.4 Or by subracting 8.4 - 5.5 = 2.9
Hope this helped you! If you need a better explaination or another example, I will be happy to help you! :)
