Come up with a linear function that has a slope that falls in the range -1 < m < 0

It's very easy to come up with linear functions if all you have to do is make sure that your slope is more than -1 and less than 0. The easier slope to choose would be -0.5. To rest of the equation (b) can be filled out as you choose:
y = -0.5x + b
b = any constant value (ex. 1, 3, 7)

2+2-9-$29: ! 3$3$282! 2! 2