Pick any two points on the graph...let's say (0 , 300) and (4,0)

To find the rate of change....Find the slope between these points : [ 300 - 0 ] / [ 0 - 4 ] = 300 / -4 = -75

This is in 100s....so the rate of change = -75 (100) = -$7500 → the value drops $7500 per year