Each arrangement is of the form VCVCVC where V stands for a vowel and C for a consonant. We can choose the three vowels {E,A,I} to go where the V's are in 3!=6 ways. For each of those 6 ways to arrange the vowels where the V's are, we can arrange the 3 consonants (D,T,L) to go where the C's are also in 3!=6 ways. So there are 6*6 or 36 ways. Edwin