It will be 5 because 4^2+3^2= 16+9=25 and then square root of 25=5
So the ratio 3:9 can be added together to make twelve. Add the number set together 3 times to get 36. Now you have 3+9 3+9 3+9. 3=blue so you will need nine blue pens and 27 red pens.
When you divide 4 by 5 you get .8 so you have to move the decimal and you get 80%.