Mary wishes to lose 5 pounds before her vacation in approximately 5 weeks. Her average consumption is 2100 kcal per day. Assuming her physical activity levels remain unchanged, she should reduce her energy intake to kcal per day.

1600 kcal/day.

Explanation:

3500 kcal = 1lb

To lose 1lb per week, you'd need to cut 500 kcal per day from your current kcal intake.

For mary, 2100kcal - 500kcal = 1600kcal per day.

At this rate, she would lose 1lb per week - if she wants to lose 5 pounds before her vacation 5 weeks from now, this would be the correct caloric intake.