Darwin used many lines of evidence to show that natural selection is the mechanism of evolution. one line was the overproduction of offspring in animal species. how did darwin believe that this affected natural selection?

I’m doing some practice exam questions for biology, and i’m not sure how to do these 3 parts to the question.

Which muscle is responsible for inhalation ?

Johnny rode his bike to a friend's house 4 blocks down the street in his neighborhood. he immediately rode back home once he realized his friend was not able to play. what was his displacement for the total bike ride? how did you determine this? what could we use as a reference point to determine he was in motion during his bike ride? why can you use it as a reference point