First step is to order the data from least to greatest.
10.5 11 11.5. 14.5 14.5 17 17 18 19
The median (Q2) is the middle number 14.5, this separates the lower half from the upper half. Q1 is the middle of the lower half, since there are an even amount of data, you have to take the average of the two middle numbers, 11 & 11.5, that would be 11.25; now we have to do the same with the upper half to find Q3, the average between 17 & 18 is 17.5
Now to find the IQR, subtract Q3 - Q1,
17.5 - 11.25 = 6.25
IQR = 6.25