Answer: 7.5 grams
Step-by-step explanation:
1 half life is the time it takes for a substance to be halved, (due to radioactive decay).
since 4 half lives have passed, we need to half the substance 4 times:
120/2 = 60
60/2 = 30
30/2 = 15
15/2 = 7.5 grams
This is an exponential decay trend, and you can use a function to graph it.
the base for that function would be 0.5