I know this sounds bad, but my 6th grader came home with a problem that doesn't make sense by how she has to show her work. Below is the problem i am...

I know this sounds bad, but my 6th grader came home with a problem that doesn't make sense by how she has to show her work.  Below is the problem i am struggling with helping her on.

30% of ___ =15

She needs to show her work by the following:

30% = 30 over 100 then divide top (30) and bottom (100) by ?? to get the answer