This reaction is called a condensation reaction. It is also known as a dehydration reaction.
When three fatty acids become attached to a glycerol molecule, a triglyceride is formed. The fatty acids become attached to the glycerol through a condensation reaction named so because 3 water molecules are formed from the 3 OH groups from the fatty acid chains and 3 H atoms from the glycerol.
The bond formed between the fatty acid chain and the glycerol is called an ester linkage.
Well it is triples you can tell that it is a division question. So triples means by 3. The equation is 2,551,500 = d X 3^6. So, now 2,511,500 / 729 is your final answer, 3,500. Hope it helps :)