All solutions here are SUGGESTED. Mr. Teng will hold no liability for any errors. Comments are entirely personal opinions.
(i)
Stratified random sampling.
Split the population of people into three mutually exclusive strata, 
Y, and 
X to be surveyed 
Number of 
latex = \frac{10000}{30000} \times 150 = 50
Z to be surveyed 
Select the required number of people within each strata using simple random sampling.
(ii)
The sample she gets will be more representative of the population since she split them into mutually exclusive strata.
KS Comments
Students can also present answers in a neat table for (i). Do take note that you must mention the use of simple random sampling.
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