Can somebody help me on probability?

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

10 ! a train starts from grand city and travels toward belleville 388 miles away. at the same time, a train starts from belleville and runs at the rate of 47 miles per hour toward grand city. they pass each other 4 hours later. find the rate of the train from grand city.

Olga used 100 ounces of flour to make 225 muffins. how many ounces of flour will be used to make 300 muffins?