Answer:
x = 27
Step-by-step explanation:
mean is calculated as
mean = [tex]\frac{sum}{count}[/tex]
sum = 2 + 7 + x = 9 + x and count = 3 , then
[tex]\frac{9+x}{3}[/tex] = 12 ( multiply both sides by 3 to clear the fraction )
9 + x = 36 ( subtract 9 from both sides )
x = 27
