out of 12 observations the 6th and 7th observations are 14 and 15 respectively find the median of all 12 observations

 Here  number of observations = 12 i.e even.
  In this case , there are two middle observations
  So median is the average(mean) of these two observations.
Here the middle observations are the $6^{th}$  and $7^{th}$ observations.
Hence median is the average of $6^{th}$  and $7^{th}$ observations
.$\therefore Median = \frac{14+15}{2}=\frac{29}{2}=14.5$