Answer
See below.
Work Step by Step
The mean of $n$ numbers is the sum of the numbers divided by $n$. The median of $n$ is the middle number of the numbers when they are in order (and the mean of the middle $2$ numbers if $n$ is even). The mode of $n$ numbers is the number or numbers that appear(s) most frequently.
Hence here the mean: $\frac{3+4+4+5+5+6+6+7+8}{9}=5.333$.
The median is the average of the middle of the sequence $3, 4,4,5,5,6,6, 7, 8$, which is: $5$.
The mode is $4,5,6$
