Science Pls help me with number 9 and 10

What is the percent by mass of oxygen in fe2o3

How many absorptions would you expect to observe in the 13c nmr spectra of the following molecules? a) 3-chloropentane b) cis-4-methyl-2-pentene

What are the advantages of using the metric system? designed as a decimal system making conversions simpler more accurate system of measurement has prefixes that correspond to an amount to use with all base units used by the entire scientific community