FATHER = 123456 
That means that each letter of father represents the following numbers:
- F = 1
 - A = 2
 - T = 3
 - H = 4
 - E = 5
 - R = 6
 
Now, 
Let's see the given code
4526 
Which letters are they representing, Let's see:
Thus, 4526 is the code for the word Hear...