How does park's decision to juxtapose salva and nya in a long walk to water us better understand each character point of view

It shows the difference between them while also bringing them together. It's a way for the reader to compare and contrast them as they both come together in the end. It makes a reader find the similarities between the two and what they want, though the way the got there is completely different and circumstantial, coming from the different eras.

hooch has about 3% alcohol content so the 5 gallon 90% platinum vodka would be stronger because it has a higher alcohol content then hooch.  

roses are red,

violets are black,

for what you said,

i hope you sit on a big fat tack.