modern physics

Given the mass of a radioactive material, phosphorus P is 0.60 g and its half-life, T1/2 is 14.3 days. i) What is the initial number of nuclei of 32p? ii) Determine the number of remaining nuclei of 32P after 20 days iii) What is its activity after 20 days? iv) Calculate the time taken for its activity to reduce to one decay per second