if you need that ratio to have lemon yellow. Find out how many gallons of yellow paint you need for every 1 gallon of white paint.
5gallons of yellow for 2 gallons of white so
5÷2 = 2.5 gallons of yellow paint for every gallon of white
multiply 2.5 by 9 , Because you need 9gallons of white paint. and you get 22.5 or 23 total gallons of yellow paint for 9gallons of white paint