General question: How do you relate power to time without knowing the mass of object being acted upon?

Specifics:
This practice problem is really bugging me:
Given:
Your max metabolic rate is 1500W (consumption of chemical energy) and your metabolic efficiency (chemical-mechanical energy) is 40%. Assume a flight of stairs is 3.5m high.

Find:
How long it takes you to run up four flights of stairs (minimum).
The answer in the back of the book is 16s.

Thanks in advance.

Question

General question: How do you relate power to time without knowing the mass of object being acted upon?

Specifics:
This practice problem is really bugging me:
Given:
Your max metabolic rate is 1500W (consumption of chemical energy) and your metabolic efficiency (chemical->mechanical energy) is 40%. Assume a flight of stairs is 3.5m high.

Find:
How long it takes you to run up four flights of stairs (minimum).
The answer in the back of the book is 16s.

Thanks in advance.