A cumulative frequency polygon (ogive) is constructed for a dataset of $200$ observations. The vertices of the ogive are given by the coordinates $(x, CF)$ as follows: $(10, 0)$, $(20, 30)$, $(30, 80)$, $(40, 150)$, and $(50, 200)$, where $x$ represents the class boundaries and $CF$ is the cumulative frequency. Using linear interpolation, what is the estimated interquartile range (IQR) of this dataset?