A frequency distribution table for the marks of 100 students is partially given. Complete the table and find the median mark.

Here's a step-by-step solution to the problem.

First, let's establish the complete frequency distribution table. The problem states there are 100 students in total.
The frequencies given in the table are:
$0 \le x < 10$: 6
$10 \le x < 20$: 9
$20 \le x < 30$: 12
$30 \le x < 40$: (This cell shows '30' in the image, but the student's work for part (a) implies this is 'y' and calculates $y=14$. There is an inconsistency here. To proceed, we will assume the student's calculation for 'y' is correct