Alright, lets get started.
We are asked to find median.
For finding median, we must arrange the given data from lowest to highest order.
So the data will be
4, 5, 10, 13
There are total 4 numbers here.
The mid of these numbers would be : 
The mid of these numbers would be : 7.5
Hence the median of these numbers would be 7.5 : Answer
Hope it will help :)