How to calculate Percentiles without alot of numbers...?

Ok, this question is killing me, i cant figure it out! What is the 84th Percentile?


What is the Approximate Standard Deviation?


This is the info provided - The distribution is a normal curve, with a mean of 100. The 16th percentile is 80. Can someone please help me out with this, just by giving a hint or the basic way to calculate this, i cant figure it out. Thanks.How to calculate Percentiles without alot of numbers...?
The normal curve is symmetric. Where is the 84the percentile in relation to the mean (50th percentile) and the 16th percentile? The computation is trivial. Does that help?

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