If the population mean is $420, what is the probability the null hypothesis will be rejected (using the rejection region you calculated above)? give your answer in the following format: 0.0450 (if it is 0.045) or 0.2345 (if it is for example 0. i. e. use 4 decimals for your answer.

The answer is the first one

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.