Respuesta :

AL2006

It seems to me that the 'blank' is after 'of', and
you're looking for the number that 15 is 25% of.

OK.  Call it 'M' (for 'Mystery number')

   25%  of  M  =  15

' 25% ' means  0.25 .
and
' of ' means 'times'.

So                                 0.25 M  =  15

Divide each side by 0.25:      M  =  60 .