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: $\frac{14+15+16+17+18+ 20+ 20}{7}=17.143$.
The median is the average of the middle of the sequence $14,15,16,17,18, 20, 20$, which is: $17$.
The mode is $20$.
