For this case we have to by definition:
1 kg equals 1000 grams
Shark 1:
405 kg and 68 grams

Thus, shark 1 weighs 405,068 grams.
Shark 2:
324 kg and 75 grams

Thus, shark 2 weighs 324,075 grams.
Subtracting we have:

Thus, shark 1 weighs 80,993 grams more than the second.
Answer:
Shark 1 weighs 80,993 grams more than the second.