Answer
See below.
Work Step by Step
The mean of $n$ numbers is the sum of the numbers divided by $n$.
The range is the difference between the largest and the smallest data value. The standard deviation of $x_1,x_2,...,x_n$ is (where $\overline{x}$ is the mean of the data values): $\sqrt{\frac{(x_1-\overline{x})^2+(x_2-\overline{x})^2+...+(x_n-\overline{x})^2}{n}}$.
Hence here the mean is: $\frac{10+12+7+11+20+7+6+8+9}{9}=10$
Hence here the range is: $20-6=14$, and the standard deviation is: $\sqrt{\frac{(10-10)^2+(12-10)^2+...+(9-10)^2}{9}}\approx4.243$
