Answer:
I used to be so generous.
Step-by-step explanation:
This can be confusing because of the pronunciation for native English speakers is very similar, however there is a correct answer.
The correct answer is almost always used, as in your example here, however in negatives and questions it is use. For example, the sentence "It didn't use to be this way," is correct compared to "It didn't used to be this way."
Hope this helps, feel free to comment with questions.