the median mark would be 67.5
this is because when you cross off one by one of the numbers on each side, you're left with 67 and 68. the middle would be 67.5
to construct a boxplot, draw a number line that will fit all the numbers you have. then make a small vertical line for 38 above the corresponding number on your number line. do this for all and connect all the median lines, leaving only the smallest and largest numbers without a connecting line.
....I hope this makes sense. if not, I'll draw it for you to demonstrate.