Smaller than 3142 are all numbers starting with "1" and "2". Than, the only number starting with 3 smaller that the one given is 3124. So, all in all, you have 6+6+1 numbers on the list that are smaller than 3142. (This means that 3142 is 14th number on the list).

Anyway, I hope that You've already managed to solve it!

best regards

katastrofa.nadfioletu