the yearly membership to the san diego zoo for a family with 2 adults and 2 children is $144. the regular admission to the zoo is $18 for each adult and $8 for each child. how many times should such a family plan to visit the zoo in a year to make a membership less expensive than paying regular admission?

Line the mark up so you will find your answer

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.