There are five boxes in cargo hold. The weight of the first box is 200 kg and the weight of the second box is 20% higher than the weight of the third box, whose weight is 25% higher than the first box's weight. The fourth box at 350 kg is 30% lighter than the fifth box. Find the difference in the average weight of the four heaviest boxes and the four lightest boxes.

Answer: Option B

Step 1: Find the weight of the third box.
The third box is 25% heavier than the first box (200 kg).
25% of 200 kg = (25/100) * 200 kg = 50 kg
Weight of the third box = 200 kg + 50 kg = 250 kg

Step 2: Find the weight of the second box.
The second box is 20% heavier than the third box (250 kg).
20% of 250 kg = (20/100) * 250 kg = 50 kg
Weight of the second box = 250 kg + 50 kg = 300 kg

Step 3: Find the weight of the fifth box.
The fourth box (350 kg) is 30% lighter than the fifth box.
This means the fourth box is 70% of the fifth box's weight.
Let the weight of the fifth box be x.
0.7x = 350 kg
x = 350 kg / 0.7 = 500 kg

Step 4: Arrange the weights in ascending order.
The weights are: 200 kg, 250 kg, 300 kg, 350 kg, 500 kg

Step 5: Calculate the average weight of the four heaviest boxes.
Four heaviest boxes: 250 kg, 300 kg, 350 kg, 500 kg
Total weight = 250 + 300 + 350 + 500 = 1400 kg
Average weight = 1400 kg / 4 = 350 kg

Step 6: Calculate the average weight of the four lightest boxes.
Four lightest boxes: 200 kg, 250 kg, 300 kg, 350 kg
Total weight = 200 + 250 + 300 + 350 = 1100 kg
Average weight = 1100 kg / 4 = 275 kg

Step 7: Find the difference in the averages.
Difference = 350 kg - 275 kg = 75 kg

Therefore, the correct option is B: 75 kg