Write and solve a real-world problem that can be modeled by the equation 0.75x-18.50=0.65x

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.