In the fig. $\text{AB,CD}$ and $\text{PQ}$ are three lines concurrent at $\text{'O'}$ . If $\overline{)\text{AOP}}=5y$ ,$\overline{)QOD}=2y$ ,$\overline{)BOC}=5y$ ,then the value of y is  

                                    

From the fig we have $\overline{)\text{AOP}}=\overline{)\text{BOQ}}=5y\left(\text{vertically}\text{opposite}\text{angles}\right)$ 

                                           $\overline{)QOD}=\overline{)COP}=2y\left(\text{vertically}\text{opposite}\text{angles}\right)$

                                           $\overline{)BOC}=\overline{)AOD}=5y\left(\text{vertically}\text{opposite}\text{angles}\right)$

We know that sum of angles around a point is $360°$

$\begin{array}{c}\overline{)\text{AOP}}+\overline{)\text{BOQ}}+\overline{)QOD}+\overline{)COP}+\overline{)BOC}+\overline{)AOD}=360°\\ 5y+5y+2y+5y+5y+2y=360°\\ 24y=360°\\ y=\frac{360°}{24}=15°\\ \text{Complement}\text{of}75°=90°-75°=15°\end{array}$