I don’t understand this at all

Idon’t have a clue on how i should understand this i’m in need of assistance.

Let r(t) represent the rate, in square feet per minute, at which a groundskeeper is mowing a lawn t minutes after 3 p.m. what expression represents the area, in square feet, of the lawn that is mowed between 3 p.m. and 5 p.m.?

When did human beings first arrive in the americas? how did they get there?