The number of words of four letters containing equal number of vowels and consonants, where repetition is allowed, is

Let us first select two places for vowel, which can be selected from 4 places in 4C2, ways. Now this places can be filled by constants in 21 x 21 ways as repetition is allowed.  The remaining two places can be filled by consonants in  4C2×25×212=150×212.