You first find two points on the graph. You then count the distance between the two y-values (vertical) then the distance between the two x values (horizontal). The slope is equal to Distance of y-values
26% less than a value is best found by multiplying by (100 - 26)% = 74% = 0.74 So previous year x 0.74 = 40,700 Previous year = 40,700 / 0.74 = $55,000