My son has missed school due to being ill and now I have to ''teach'' him how to do his math work. I am familiar with rounding and estimating but they have introduced new ways to estimate which in turn confuse me. So I am going to scan the math problem and attach it on here. Please please please help me understand what this question is asking. I have looked and searched for help and even the textbook website doesn't explain this stuff where I can understand.

Question # 21:
Write a problem using estimation and subtraction. Use the table at the right. Tell which method you would use to estimate the difference. Explain your choice.

Sea Turtle
Weight In Pounds
Loggerhead 185
Hawksbill 125
Leatherback 779