How to calculate body fat percentage

[Cloud 9]

Homework Statement

A 180 lb man weighs 5 lb in water. What is his percent body fat? Assume that fat has a density of 0.90 g/cc and muscle has a density of 1.06 g/cc. Water has a density of 1.0 g/cc.

Although we are given the weight in lbs, it is okay to work with it like mass (as grams) or even as buoyant force...why?

Is this bc both sides of the equation (mass of fat and mass of muscle) will be in the same unit, so it doesn't matter?

What is the total mass? m-total = m-muscle + m-fat

This was the first question of a series of questions and I don't understand how we can calculate the mass without a volume...I don't understand the relationship between the weight and volume displaced.

 

[haruspex]

Yes, all forces in the question arise as mass * gravitational acceleration, so the gravitational acceleration cancels out.
Can you state Archimedes Principle, and see what it tells you about the man's volume?