If each observation of a given set of data is increased by 5, their mean:

1. remains the same

2. becomes five times

3. is decreased by 5

4. is increased by 5

26, x + 4, x + 2 and 18 are in descending order of their values and their median is 20, then the value of x is :

1. 19

2. 17

3. 15

4. 13