The correct option is C 30 - 10 = 20
If Rinee has 28 mangoes with her and if she eats 9 of them, to find the remaining number of mangoes, we need to subtract the rounded off values
28 mangoes can be rounded off to 30 mangoes
9 mangoes can be rounded off to 10 mangoes
30 - 10 = 20
The correct option is C