First, reorder the numbers for each person. The median is basically the middle number. If there are 2 middle numbers, then take the average of the two of them.
Pedro: 4, 5, 6, 7, 8, 9 The 2 middle numbers are 6 and 7. The average of 6 and 7 is 6.5 . Median = 6.5
Alex: 3, 5, 5, 5, 9, 9 The 2 middle numbers are 5 and 5; so basically, the average is 5. Median = 5
Jaime: 3, 4, 6, 8, 8, 9 The 2 middle numbers are 6 and 8 and thus, the average is 7. Median = 7