#### Answer

$$mean = 0$$
$$median = 0$$
$$mode = none$$

#### Work Step by Step

To calculate the mean, sum the data values in the set and divide by the number of data values in the set:
$$mean = \frac{-4-3-2-1+0+1+2+3+4}{9}=\frac{0}{9}=0.$$
The median is the middle value of the data set when it is arranged in increasing or decreasing order:
$$-4,-3,-2,-1,0,1,2,3,4.$$
So
$$median = 0.$$
The mode is the value which occurs most often in the data set. Since each of the values occurs only once, there is no mode.