One of the byproducts of nuclear power generation is uranium-233. uranium is decaying at a constant 32% rate per day. if 12,880 pounds are produced from a power plant, what will the amount be in 20 days?

a 21.4009
b 644.208
c 6955.200
d 8243.563

We make use of the equation,
                                amount in days = original amount x (1 - rate of decay)^ n
where n is the number of days. 
Substituting the known values,
                           amount = (12,880 lbs) x (1 - 0.32)^20
                                        = 5.755 lbs
The answer should be 5.755 lbs which is not among the choices.