Answer:
50 oranges
Explanation:
First we need to know the conversion measure.
1kg=1000grams
And if a box is 4kg heavy, it means only oranges weighing 4 times 1000grams can fill it up.
If an orange now weigh 80grams. It means how many oranges will measure up to 1000grams.
1000/80 = 50
50 oranges, each weighing 80grams will fill up a box to weigh 4kg