If you have 7 divided by 21 . And u have to have a whole number what's the answer

7/21 isn't going to give you a "whole" number....ever !!!

I suspect you want something in a non-fractional form.......

.333  should do the job, here.....[the 3's actually repeat......forever!!!.....but, we'll call it good at 3 digits  !!! ]

7/21  =  1/3

You can round this answer; if you do, it becomes 0.

If you must have a non-zero answer, the closest whole number greater than 0 is 1.