Approximate the Number Using a Calculator $f ( x ) = 500 ( 0.5 ) ^ { x / 100 }$

Approximate the number using a calculator. Round your answer to three decimal places.
-The function $f ( x ) = 500 ( 0.5 ) ^ { x / 100 }$ models the amount in pounds of a particular radioactive material stored in a concrete vault, where $x$ is the number of years since the material was put into the vault. Find the amount of radioactive material in the vault after 140 years. Round to the nearest whole number.

A) 189 pounds
B) 305 pounds
C) 350 pounds
D) 179 pounds