The NaCl LD₅₀ dose is 3000 mg / kg body mass.

The weight of  the 100 pound person must be converted to kilograms.

100 pounds  x  ( 1 kilogram / 2.2 pounds) = 45.4 kg

This mass is multiplied by the LD₅₀ dose. This multiplication gives the total amount that will meet the threshold for the 100 pound person.

The mass of NaCl that would produce the total mass to reach the LD₅₀ is

(45.4 kg body mass) x (3000 mg / 1 kilogram body mass) = 136,200 milligrams NaCl

This is 136 grams of NaCl or about 1/4 of a pound of sodium chloride, NaCl.