During one hour at an amusement park, 20 guests bought only day passes, 60 guests bought only tickets to individual rides, and 40 guests bought only food.

What percentage of these 120 guests bought only day passes during this hour?
A
80%
I
B
20%
с
83%
162%
D

So the first thing we do is to multiply the top equation by 3. the reason i want to do this is i notice there will be a 6y on both equations and can possibly add/subtract them. so we get 6y = -3x + 27. adding that and the second equation we get 6x = 27-15 which is 12. divide by 6 and we get 2. ∴ x = 2. substituting 2 into the first equation we get 2y = -2 + 9 which is 7. divide by 2 and we get 7/2. ∴ y = 7/2, x = 2.