102125
First letter count in the alphabet is first digit i.e. J --> 10
Last letter count in the alphabet is first digit i.e. Y --> 25
Now see this logic
January -- First Vowel is a so middle digit is 1 (but repeated so 10)
February -- First Vowel is e so middle digit is 5
March -- First Vowel is a so middle digit is 1
April -- First Vowel is i so middle digit is 9
May -- First Vowel is a so middle digit is 1
June -- First Vowel is u so middle digit is 21
July -- First vowel is u so middle digit is 21
hence number is 102125