What type of money did the greenpack party recommend?

Easy

Actually the Greenback Party recommended the paper money. But in the given options the easy money refers  to a money that could be easily regulated. Other forms of money such as gold coins cannot be regulated easily. A small amount of loss can result a huge turmoil while in the form of paper money it is just an alternative to the real assets. Paper money can be replaced by other notes if the previous notes are torn and damaged where the actual assets are not disturbed.

necessary and proper clause. the congress shall have power to all laws which shall be necessary and proper for carrying into execution the foregoing powers, and all other powers vested by this constitution in the government of the united states, or in any department or officer thereof.