Half life help!

Question

Tritium is a radioactive form of hydrogen with a half life of 12.3 years. How much of the 48.0 mg of tritium is still radioactive after 98.4 years? Round to the correct number of significant figures and use units (mg)

Answer 1

If the half live is 12.3 and 98.4 years have passed this is 8 half lives so of the original amount of 48.0 mg. we would have ..188 mg left.