Answer:
12
Explanation:
The missing number can be calculated by using the formula:
mean = (sum of data)÷(number of data points)
15 =
90 = 18+16+x+9+12+23
x=90-18-16-9-12-23
x=12
To check, just take the mean while including the found value for x:
mean =
=
= 15