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)