The jelly junior high school color is made by mixing red paint with yellow paint. the ratio of red to yellow is 3 to 5. how much red paint should be mixed with 20 oz of yellow?

If we want to use red to yellow in ratio 3:5 and we know we have to use 20 oz of yellow we can say that our 5 from the ratio represents 20 oz. So we can divide it by 5 to find how much oz is 1 and then multiply it by 3 to find amount of red.
20:5=4 [oz] 
4*3=12 [oz] - amount of red

The answer would be: b