Input (grade 13): His intention was to attach a few helium-filled weather balloons to his lawnchair, cut the anchor, and then float above his backyard at a height of about 30 f for several hours.
Output (grade 5): He planned to attach a few large balloons filled with helium to his lawnchair and then float above his backyard. He planned to stay about 30 feet up in the air for several hours.