To calculate the range of a set of numbers you have to calculate the difference between the maximum value and the minimum value.
In the first step you have to order the values from least to greatest to determine the minimum and maximum values:
-25, -22, -21, -20, -17, -17,-17, -15, -14, -12
The minimum value of the set is -25 and the maximum value is -12
The range of the data set is 13.