The correct option is
A J165
The given sequence is A30, D75, G120.
The numbers in the code are in increasing order.
Difference between the 2nd and the 1st terms = 75 - 30 = 45
Difference between the 2nd and the 3rd terms = 120 - 75 = 45
Hence, the number in the next term is 120 + 45 = 165
Let us find the relation between the letters in the terms.
Here, the letters are equivalent to the numbers 1, 4, 7.
Hence, the next number should be 10 and the equivalent letter is "J".
Hence, the next code is J165.