Answer:
LEAST DIFFICULT: B
MOST DIFFICULT: I
Step-by-step explanation:
LEAST DIFFICULT:
The easiest systems of equations to solve are ones in which x or y is equal to just a number , because in this case, you can just sub in that number in the other equations. Though not the only one, B is an example of this.
MOST DIFFICULT:
More difficult systems of equations to solve are the ones with different amounts of x and y as it requires more computation. Set I is an example of this
i think the answer is 1.6*10^-3
The GCF (Greatest Common Factor) is 6a.
When you divide 6x10^24 by 8x10^8 you end up with 
This simplifies to 
Now this number is not written in scientific notation as it does not have its first digit before the decimal, so we must move the decimal of this one to the right.
To do that you must multiply the number by 10.
This means that the exponet of 10 must decrease by 1.
This makes the answer 
I believe the answer is D
if you fold it all together using the dotted line, it looks that it will all fit together and look like the above shape
hope this helps