Analyzing a sample list of numbers (median, quartiles, box plot)

#1
If you have a sample of 36 numbers (and some of these numbers are repeated more than once), how do you find the median, upper quartile, and lower quartile of the sample?

Also when drawing a box plot, do you disregard when a number is shown more than once and just put it down once in the plot?
For example you have 21, 24, 26, 26, 26, 29, 31, 35, etc...

Would the box plot show up as 21 24 26 29 31 35...?
 
#2
The average is just the sum divided by the number of values (36). The median is just the very middle number (or the average of the middle 2 numbers). The quartiles represent the value for which a certain % lie above or below that value.
 
#3
The average is just the sum divided by the number of values (36). The median is just the very middle number (or the average of the middle 2 numbers). The quartiles represent the value for which a certain % lie above or below that value.
How would I calculate what the upper and lower quartiles are? Wouldn't the lower quartile be half way between the lowest number and the median, and the upper quartile be half way between the median and the highest number?