### Instruction: The mean (average) of 6, 9 and 18 is equal to the mean (average) of 12 and $y$. What is the value of $y$?### Response: To find the mean (average) of a set of numbers, I need to add them up and divide by the number of elements.
So the mean of 6, 9 and 18 is $\frac{6+9+18}{3} = \frac{33}{3} = 11$.
Similarly, the mean of 12 and $y$ is $\frac{12+y}{2}$.
Since the problem says that these two means are equal, I can set them equal to each other and solve for $y$: $\frac{12+y}{2} = 11$.
Multiplying both sides by 2, I get $12+y = 22$.
Subtracting 12 from both sides, I get $y = 10$.