What is the median of the first 15 multiples of 4?

The numbers are 4, 8, 12, … , 60. With 15 of them the median is the single 8th value, which is $8\times 4=32$. Because the numbers are evenly spaced the mean lands there too, being the average of the first and the last, $(4+60)/2=32$ — for an evenly spaced list the mean and the median always agree. The values 28 and 36 are the 7th and 9th terms, reached by counting the middle position wrongly, and 30 is half of the largest term, which has nothing to do with the middle of the list.