If the first worker's marginal product is 19 hamburgers that means that only 19 hamburgers are procused. Than when the second worker occurs the marginal product is 32 and it means that both workers produce 32 more hamburgers together, so total amount of hamburgers is "19+32=51." And after the third worker is employed, the total production is "51+29=80."
"AProduct= TProduct\/Labor" .
"AP = 80\/3=26.66"
So, the average product of labor is 26.66 .
If the fourth worker's marginal product is above the average, then the average product of labor will increase.