Al is at the point (0,6) and Bob is at the point (8,0). They are both running towards the origin. Al is running at 2 units/s and Bob is running at 4 units/s. In this moment, how fast is the distance...

Extracted text: Al is at the point (0,6) and Bob is at the point (8,0). They are both running towards the origin. Al is running at 2 units/s and Bob is running at 4 units/s. In this moment, how fast is the distance between Al and Bob changing in units/s. Note: your answer should be negative.