Question

Della was slender. she mastered the art (change into simple compound) ​

Answer 1

Answer:

Della was slender and had mastered her art.

(Compound sentence)

Being slender, Della had mastered the art.

(Simple sentence)

Hope it helps you.

Answer 2

Answer:

Ur question : Della was slender ,she mastered the art. ( it is compound sentence)

And Hello dear mate. ur answer is like this

Answer: Being slender , Della had master the art

and it is now in simple sentence

I hope it helps you and others.