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Answer: 
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n starts at 1, and n is a positive whole number (1,2,3,...)
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Explanation:
The sequence is arithmetic with first term 40 and common difference 10. Meaning we add 10 to each term to get the next one.
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a1 = 40 = first term
d = 10 = common difference

is the general nth term of this arithmetic sequence
Plug in n = 1 and you should get 
Plug in n = 2 and you should get 
and so on
The ratio would be 90pi/40pi.
Hope this helps:)
I believe you have to do a cross product formula.
2174/x = 28.19/100
Do this and then simplify the result
Picture needed. not enough info