How many half-lives have passed if 40 grams are left when the sample started with 160 grams?

1.solid

2.carbon dioxide

3.helium

a pan containing water is placed in a positio n where it is exposed to a 10 mile per hour wind. the pan contains a uniform depth of 1.27 cm of water, is quite wide, and has a length of 2.44 m in the wind direction. the water in the pan is at a constant temperature of 15.5 °c.