Answer: 
Step-by-step explanation:
I hope you mean y = x² - 12 and not y = 2x - 12.
You switch the y and x variables:
x = y² - 12
And solve for y:
x + 12 = y²

Answer:

Step-by-step explanation:
It will need to be 9 as 27 by 8 is 216 and 23 by 9 is 207 and the you subtract 207 from 216 and get 9