Daniel put water, sugar, and yeast into a balloon. then he measured the mass of the balloon. he put the balloon in a warm place for 2 hours. then he measured the mass again. he repeated his experiment three times to get more data. predict how the mass of the balloon changed.

During the period of 2 hours, the yeast ate the sugar, and generated Carbon-Dioxide gas and alcohol.  This is the process that causes bread-dough to rise, and eventually produces stuff that can be distilled to concentrate the alcohol and make wine or whiskey.

-- If Daniel tied the neck of the balloon, so that nothing could get in r out during the 2 hours, then the mass of the balloon and everything inside it didn't change.  The balloon may have inflated slightly ... due to the creation of gas inside that wasn't there before ... just like bread dough.  But no mass was created or destroyed inside or outside of the balloon, and none got in or out.

-- If Daniel left the neck of the balloon open, then the mass of the balloon and its contents decreased slightly during the 2 hours.  The yeast took carbon and oxygen from the sugar, and used them to make Carbon Dioxide gas.  Then the gas flew out through the neck of the balloon to Freedom.