Final answer:
Melissa should bend her knees as she lifts the boxes, and she should inform the clerk that she cannot help him move the boxes if her job does not require heavy lifting.
Step-by-step explanation:
Melissa should make sure to bend her knees as she lifts the boxes. This is because using the large muscles of the legs to lift objects helps to prevent back injuries. According to the safety manual, employees should avoid using the smaller muscles of the back and instead focus on using the legs to lift heavy objects. Melissa should also tell the clerk that she cannot help him move the boxes if her job does not require heavy lifting. This is because workers who do not hold jobs that require heavy lifting should not be asked to perform this task. Lastly, wearing a safety belt would not be necessary to help out the clerk, as the manual does not mention this as a safety precaution for lifting heavy objects.