NDA Math Permutations and Combinations

2nd and 4th place are even place, so vowel ′A′ and ′E′ arrange either 2nd or 4th place in 2!=2×1=2 ways.
Consonent letter, ′B′ and ′L′ arrange at 1st and 3rd place in 2!=2×1=2 ways.
Total number of arrangement =2×2=4.