preschool children can solve this
8819 = 5
1777 = 0
7155 = 0
6172 = 1
0000 = 4
5525 = 0
8989 = 6
1010 = 2
9669 = 4
2528 = 2
7776 = 1
5172 = 0
2851 = ?
8819 = 5
1777 = 0
7155 = 0
6172 = 1
0000 = 4
5525 = 0
8989 = 6
1010 = 2
9669 = 4
2528 = 2
7776 = 1
5172 = 0
2851 = ?
