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: $\frac{2+3+4+6+7+8+8+9+12+15}{10}=7.4$.
The median is the average of the middle two in the sequence $2,3,4,6,7,8,8,9,12,15$, which is: $(7+8)/2=7.5$. The median is 7.5.
