All solutions here are SUGGESTED. Mr. Teng will hold no liability for any errors. Comments are entirely personal opinions.
Case 1: 2 same letter and 2 different digits
Case 2: different letter and 2 same digits
Case 3:3 same letter and 2 same digits
Case 1: 2 different consonants, 1 vowel & 1 even digit
Case 2: 2 same consonant, 1 vowel & 1 even digit
This question is not that easy. A lot of thinking is required; but that is the case with all permutation questions. I strongly suggest students to not spend too much time on permutation questions and come back to solve it later.