Answer:
56
......................................................
90 + 20x + 10x = 180
30x = 90
x = 3
Answer:
9
Step-by-step explanation:
i hope this is helpful........
The amount of substance left of a radioactive element of half life,

after a time, t, is given by:

Given that <span>potassium-40 has a half life of approximately 1.25 billion
years.
The number of years it will take for 0.1% of potassium-40 to remain is obtained as follows:

Therefore, </span><span>the maximum age of a fossil that we could date using 40k is
12.5 billion years.</span>