A scuba diver is 30 feet below the surface of the water 10 seconds after he entered the water and 10

A scuba diver is 30 feet below the surface of the water 10 seconds after he entered the water and 100 feet below the surface after 40 seconds later. At what rate is the scuba diver going deeper down in the water

If we take these as coordinates on a graph, where y is the depth and x is the time, we calculate our slope or rate of change where (x1, y1) = (10, 30) and (x2, y2) = (40, 100)
Rate of change = (y2 - y1)/(x2 - x1)
Rate of change = (100 - 30)/(40 - 10)
Rate of change = 70/30
Rate of change = 2.333 feet per second