Let's assign three blanks for each digit of the unknown number. But let's fill in the tens digit because it is already specified.
_ 4 _
The last digit should be even to make it even. The possible digits for this are 2, 4, 6, and 8. The first digit could be any digit from 1 to 9. Therefore, the possible answers are
142 242 342 442 542 642 742 842 942
144 244 344 444 544 644 744 844 944
146 246 346 446 546 646 746 846 946
148 248 348 448 548 648 748 848 948
Therefore, there are a total of 36 possible answers.
