Answer:
The answer to your question is: Â 128 days
Step-by-step explanation:
Data
original mass = 21 g
after 45 days = 17.3 g
Process
mass transform = 21 - 17.3 = 3.7 g
       Â
                21 g ----------------------- 100 %
                3.7 g ---------------------  x
                x = (3.7 x 100) / 21
                x = 17.61 %
                17.61 % -------------------  45 days
                50%   --------------------  x
               x = (50 x 45) / 17.61
               x = 127.8 ≈ = 128 days
