HELP ASAP Element X is a radioactive isotope such that every 20 years, its mass decreases by half. Given that the initial mass of a sample of Element X is 770 grams, how long would it be until the mass of the sample reached 400 grams, to the nearest tenth of a year?

Will make ! for correct answer the dot plot below shows the number of toys 21 shops sold in an hour.is the median or the mean a better center for this data and why? a. median; because the data is not symmetric and there are outliersb. median; because the data is symmetric and there are no outliersc. mean; because the data is symmetric and there are no outliersd. mean; because the data is skewed and there are outliers