Answer:
11
Step-by-step explanation:
The mean is calculated as
mean = [tex]\frac{sum}{count}[/tex]
let the third number be x , then
[tex]\frac{18+16+x}{3}[/tex] = 15 ( multiply both sides by 3 to clear the fraction )
34 + x = 45 ( subtract 34 from both sides )
x = 11 ← third number
