Diana had chocolate, and ate some, leaving 0.75 of it for Sarah.
Sarah ate 18.5 grams of it and return the rest to Diana, which was 65% of the original chococate.
how much chocolate did Diana have at the beginning?
and the solution is:
0.75x-18.50=0.65x
0.75x-0.65x=18.50
0.1x=18.50
x=185
so Diana had 185 grams of chocolate.
Hope this helped