Answer: B (65%)
Explanation:
Let's start with what we know. Since your sister has 80 cupcakes and she gave you 28, that means she kept 52 for herself. So she has 52 of the total 80 which can also be written as:
52/80
This can be simplified to:
13/20
Now when getting percents we need to make the fraction something/100 so to do that with this fraction we can just multiply by 5 to get:
65/100
So the percent is B) 65