Given that a certain shade of pink is created by adding 3 cups of red paint with 7 cups of white paint.
That means ratio of red paint and white paint must 3:7 .
Let x be the amount of red paint cups for 1 cup of white paint.
Then ratio of red paint to white paint is
Hence cups of red paint is needed for 1 cup of white paint.
The number in "?" is or 0.04286 cups.