Hi there!
We can begin by splitting the data into two equal parts, ignoring the median.
The median is simply the number in the middle of the data, or 5.
Now, we can split the data, taking the three left numbers and the three right numbers.
We have:
Left: 1, 3, 4
Right: 5, 7, 9
Find the medians of these sections. These are the middle numbers again, so:
Left: 3
Right: 7
These are our 1st and 3rd quartiles, respectively. The IQR is the difference between these, so:
7 - 3 = 4 = IQR.