Question says that Isabelle is mixing red paint with blue paint to make purple paint.
She adds 3/10 of a fluid ounce of red to 11/16 fluid ounces of purple.
Now we need to find about how many fluid ounces of red will she need to make 3 fluid ounces of purple paint.
So let we need x fluid ounces of red color paint.
To find that we can setup ratio between quantity of red and pruple colour paints.
Hence final answer is fluid ounce of red colour.