Use the 3x3 Prewitt mask to calculate the gradient at the red circled location. 2) Use the 3x3 Sobel mask to calculate the gradient at the green circled location. 50 40 70 130 160 150 y 60 30 130 140 150 140 70 80 50 150 160 170 130 170 70 35 60 30 140 150 140 180 70 150 150 160 170 30 40 50