Emry weighed her empty backpack with a spring scale. She found that the pack weighed 8.1 N. Suppose she picks up her backpack from a desktop and lifts it through a height of 42 cm. How much gravitational potential energy does the backpack gain? (show the steps you followed to solve the problem - ie. the formula, calculations, and final answer) ROUND YOUR ANSWER TO 1 DECIMAL PLACE.