17. 2x<16 x=7 or lower
All I can help you with is #17,
sorry that I can't answer the other 3.
I hope this helped! :-)
X=0 because when you have something to the power of zero your answer is 1.
x=0 since 1 to the power of zero equals 1.
hope im not too late
Answer: 
Each term is half of the previous one, so the common ratio is 1/2. Then to get from the first term to the nth term, you have to take n - 1 steps, multiplying by 1/2 each time and by 6000 to account for the first term.
i hope this helps! :D