The universe cooled after the big bang. at some point, hydrogen atoms combined to form helium. what is this process called?

This process is called as Nuclear Fusion

In the basic Hydrogen fusion cycle, four Hydrogen nuclei (protons) come together to make a Helium nucleus. This is the simple version of the story. There are actually electrons, neutrinos and photons involved that make the fusion of Hydrogen into Helium possible.

You would do 1500/4 and the answer is 375

The answer is b because c don't explain why the moths are on them and it isn't a because as we know only one species of moth does this