A Uniform Wooden Plank Floats in a Swimming Pool

Multiple Choice

A uniform wooden plank floats in a swimming pool. The plank weighs 100 pounds, and exactly 10% of its volume is above the waterline. The maximum weight of iron which could be suspended from underneath the plank without causing the whole combination to sink to the bottom of the pool is

A) exactly 10 pounds.
B) somewhat more than 10 pounds.
C) somewhat less than 10 pounds.
D) more information is needed.