Help me I got 25 missing assignments

Determine whether the set of whole numbers is closed under addition. explain why the set is or is not closed. give an example.

He ! a group of farmers planned to clean 80 acres of wheat per day to finish the work on schedule. right before the work started, they received a new piece of machinery that them clean 10 more acres per day than originally planned. as a result of increased productivity in the last day before the deadline they only had to clean 30 acres. how many acres of wheat did the group of farmers have to clean?

Which strategy is used by public health to reduce the incidence of food poisoning?