OMG! I wish I still had this math! You see if each second the rock goes 5 feet away from the surface. After 4 seconds it will have been 20 feet below the surface. But if Lisa dropped it 5 feet above the surface than after 4 seconds the rock would be 25 feet below the surface.
The rule for 90 degree clockwise rotation is (x,y) turns into (y,-x) therefore if you use your numbers (2,-6) and then use the 90 degree clockwise rotation rule it becomes (-6,-2)
