To make purple paint, you need 3 parts red and 5 parts blue. How much red paint is needed if I use 20 ounces of blue paint?

12 Parts Red

Step-by-step explanation:

5*4=20

3*4=12

12 Parts Red

check above link.

graphically?   well, you graph them both, the solutions is where they both intersect each other, since there are two solutions, meaning they will meet twice, or namely the linear will run into the quadratic curve twice, and where they meet, those x,y coordinates are the solutions to the system.