Answer:

Explanation:
Let's use the decay equation.

Where:
- A is the activity at t time
- A₀ is the initial activity
- λ is the decay constant
We know that 
So we have:




Therefore, the half-life of the source is 6 hours.
I hope it helps you!
<span>The land between two normal faults moves upward to form a
Answer:D</span><span>
fault-block mountain.</span>
The great astronomer of ancient times who summarized and improved...in a book now called The Almagest) is Ptolemy This is further explained below.
<h3>Who is Ptolemy?</h3>
Generally, Claudius Ptolemy was a Greek mathematician, astronomer, and geographer who lived in the second century CE and is best known for proposing the geocentric model of the cosmos, which was used to explain planetary and stellar movements for the next thousand years.
In conclusion, Ptolemy, the ancient world's preeminent astronomer, compiled and refined a system of circles inside circles to describe the complexities of planetary motion, publishing his work in what is now known as The Almagest.
Read more about Ptolemy
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