How many units of red paint should be mixed to get shade of pink if have 3 units of red paint with 8 units of white paint to get pink?

Depends on how much paint you want, If you want 11 gallons, three gallons of red are needed.

If you have two gallons of white paint, you'll need three quarts of red paint.

Take however much you need to do the job, divide that amount by 11, multiply that total by three and that will tell you how much red paint you need.