Step 1: Divide the number into separate digits:
7057 => 7 0 5 7
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
7 to 0 = 7
0 to 5 = 5
5 to 7 = 2
7 to 7 = 0
Step 3: Combine the filters to a string:
7 5 2 0 = 7520