Answer: x = 21
Step-by-step explanation:
For this problem we can simply write an equation to solve for the value of x. We know that the average (sum divided by count) is equal to 18. So let’s leverage this to solve for x.
( 12 + 21 + x ) / 3 = 18
12 + 21 + x = 18 * 3
33 + x = 54
x = 54 - 33
x = 21
Hence, we have found the value of x to be 21.
Cheers.