Answer:
1.5 years
Step-by-step explanation:
The half life of substance A is 0.5 years, or 6 months. If the initial mass of substance A is 16, grams, then in 6 months it will become 8 grams. In another 6 months, it will become 4 grams. This means that in the space of a year, substance A has lost 12 grams. In another 6 months, it would halve to 2 grams which is the remaining number.