Design a zoo, anyone has the answers to this project?

A80-foot piece of siding is cut into three pieces so that the second piece is four times four times as long as the first piece and the third piece is five times as long as the first piece. if x represents the length of the first piece, find the lengths of all three pieces.

What's the difference between: x≥0 and nonnegative integer. ?

Which of the following is the result of expanding the series