In doing the exercise, I wrote: "des robe aux silhouettes cintrées..." and it was crossed out and corrected to "cintrés" with only one "e". As "silhouette" is feminine, "cintrées" should be the right answer, and I see that it is written as such in the full text at the end of the exercise.
Otherwise, as usual, an enjoyable exercise where I learned a new word: "cintré(e/s)!
Merci
N.Hilary