First, you want to put all the numbers in order from least to greatest.
21, 33, 33, 42, 67, 79, 89
Now, you can use this song to help remember how to do these problems.
Cross off the sides till you get to the center. 1 is good, 2 is bad. (If you get two numbers in the middle) add then divide by two.
Cross off 21, then 89, then 33, then 79, then 33, then 67. Now, you're left with 42 in the middle. That is your median. Hope this helps! :)