The distribution of weights of a large group of high-school boys is normal with a mean of 120 pounds and a standard deviation of 10 pounds. What is the probability of a randomly selected high-school boy will have a weight of at most 145 pounds?

Ihave, but this question is gonna probably get deleted.

Is it multiple choice

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.