first, arrange the data:
20, 21, 24, 25, 28, 29, 35, 37, 39, 42, 44
You can use the formula 3/4 multiplied by the number of data + 1 to find the position of the 3rd quartile.
so it's going to be 3/4 x (11+1) = 9th position
the number in 9th position is 39 so that's the 3rd quartile
