So the sum of both deserts is 30000000 and one is 9 times more than the other, it’s a 1:9 ratio. 9+1 is ten and 30000000/10 is 3,000,000. That’s the area of the smaller desert. You multiply 3 million by 9 and get 27,000,000 sq miles for the larger desert. Hope that makes some sense! :)