Answer:
A)
B) 
Explanation:
A) Using the Archimedes' force we can find the weight of water displaced:

Where:
: is the weight of the block in the air = 20.1 N
: is the weight of the block in the water = 15.3 N

Now, the mass of the water displaced is:

The volume of the block can be found using the mass of water displaced and the density of the water:

B) The density of the block can be found as follows:

I hope it helps you!
The process that powers stars is C)fusion
It's been a while since I've studied this, but my answers would be:
13. 5730 years. The half-life of a substance is the amount of time it takes for half of it to decay, and, according to the graph, half of the substance remained at 5730 years.
14. 10740 years. According to the graph, only 25% of the carbon remained after 10740 years.
15. 15 atoms. According to the graph, only 12.5% of the carbon remained after 16110 years. 12.5% of 120 atoms is 15 atoms.
16. 1600 atoms. According to the graph, if a sample of carbon is 10740 years old, only 25% of it remains. To find the original amount, multiply the current amount by (100% / 25%), which equals 4. So, 4. 400 atoms * 4 = 1600 atoms is the original amount.