First you would add together the ratios which equals 9. Then divide 1,800,000 by 9 giving you 200,000.Then you would multiply 200,000 by each ratio individually giving you the answers. which would be 800,000:600,000:400,000
It would be great if you added some more details, but for common denominators you try to find the least common number that the 2 or more of the numbers you got have! For example: 1/2 and 2/3 if you multiply 2 by 3 and 3 by 2, they both are 6, so you would multiply 1/2 both by 3 to make it into 3/6 and 2/3 by 2 to make it into 4/6!