Blow Up a Guest Mattress, Fill It With Air
Puzzle 20 of Buying Books Piece of Cake Pack
Question is: Blow Up a Guest Mattress, Fill It With Air
and the answer is: INFLATE
Word Meaning:
INFLATE — (transitive) To enlarge an object by pushing air (or a gas) into it; to raise or expand abnormally
Definitions from Wiktionary.