I am having difficulty figuring out how the answer to this question is 40 per the solution on the gmat practice test. I set up the ratio 5x:3x... I then set up the equation of 7/5= x/10+x to come up with X, but that is where I am stuped..Help please!!

Here is the question:

The number of stamps that kaye & Alberto had were in the ratio of 5:3 respectively. After Kaye gave Alberto 10 of her stamps the ratio Kaye had to the number Alberto had was 7:5. As a result of the gift, Kaye had how many more stamps than Alberto?

The choices were : A-20, B-30, C-40, D-60, E-90

K/A = 5/3
3K = 5A
3K - 5A = 0
15K - 25A = 0


(K - 10)/(A + 10) = 7/5
5K - 50 = 7A + 70
5K - 7A = 120
15K - 21A = 360


15K - 25A = 0
15K - 21A = 360

- 4A = - 360

A = 90

15K - 25(90) = 0

15K = 25*90

K = 25*90/15 = 150


K - 10 = 140

A + 10 = 90

140 - 90 = 50

Veritas Help

the answer is D, because A = 90 (as stated above by VeritasHelp), and K = (A*5)/3 which means K = 150.

The question asks "how many MORE", so final answer would be 150 - 90 = 60. D.