Answer:
Egg yolks contain far more protein and fat than egg whites do.
Step-by-step explanation:
A complete sentence has to have a subject, a verb, and a complete thought. That last part is going to be important as we rule out the second sentence.
The phrases "Multiplying fractions and decimals isn't hard" and "I can show you how" are two completely different thoughts. You can't just add a comma after a complete thought and then stick a different one after it. You have to add a conjunction or ";" symbol.
So, we can say that the second sentence is not a complete sentence since it has two different complete thoughts that aren't joined together properly.
The first sentence has a subject (egg yolks), a verb (contain), and it is one complete, whole thought, so it is a complete sentence.
Hopefully this was helpful! If you need further help, let me know.