The half-life of cobalt -60 is 5 years if you have 10 grams of co-60 how much do you after 15 years

Every 5 years it will be half.  So

After 5 years = 10/2 = 5 grams

After 10 years = 5/2 = 2.5 grams

After 15 years = 2.5/2 = 1.25 grams

as in mitosis, dna replication occurs during interphase.   in meiosis, it occurs specifically in s phase of interphase 1.