Answer:
302
Step-by-step explanation:
420(grams per sec)x60(seconds in a min) = 25,200(grams per min)
25,200x60(min in an hour) = 1,512,000(grams an hour)
1,512,000/1,000(grams in a kilogram) = 1,512 (kilograms per hour)
1,512/20 (size of bag) = 75.6 (bags filled per hour)
75.6x4(hours elapsed asked by the question) = 302 bags completly filled in 4 hours
