what is the function rule? X=-2,-1,0,1,2 y=9,4,-1,-6,-11

Every time that the x-value increases by 1, the y-value decreases by 5.

A formula can be:  y  =  -5x - 1.

The amount of decrease is 5 means that the slope is -5; when x = 0, y = -1 means that the y-intercept is -1.