Question

Nickel 63 half life of 92 years. how much nickel 63 world reamin in a sample containing 20 micrograms of nickle 63 at the end of 184 years

Answer 1

184:92 =2 half lives.

Initial mass of Ni is 20 micrograms (μg).

After one half-life 20*1/2=10 μg remain,
after second half-life 10*1/2 =5 μg remain.

So, after 184 years  5μg of Ni-63 remain.