Asample originally contains 21 grams of a radioactive isotope. after 45 days, 17.3 grams of the isotope remain in the sample.

what is the half-life of the isotope?
round your answer to the nearest day

The answer to your question is:  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

                                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