Phosphorus 32 has a half life of 14.3 days how much of a 4 mg sample of phosphuros 32 will remain after 71.5 days

After each half-life, half of the original sample will remain. 
Therefore, in 71.5 days, taking into consideration that a half-life is 14.3 days, there will be 5 half-lives. 
Therefore, we split 4 in half, then in half again, etc. five times.
4 ⇒ 2 1st half-life
2⇒ 1 2nd half-life
1 ⇒ 1/2 3rd half-life
1/2 ⇒ 1/4 4th half-life
1/4 ⇒ 1/8 5th half-life

Therefore, 1/8 m of the sample will remain