So the ratio is 7:5 and the total profit is 90$ so if you added 7 and 5 together you would get a total of 12 parts and if you divided 90$ by 12 you would get 7.5 ... so if you take the 7.5 back into the original 7:5 ratio and times it by each term/ 7.5 x 7 = 52.5 , 7.5 x 5 = 37.5 / add the two totals together/ 52.5 + 37.5 = 90 (the original total profit)