18 = 1 × 2 × 3 × 3 = 21 × 32
12 = 1 × 2 × 2 × 3 = 22 × 31
LCM of 18 and 12 = 22 × 32 = 36
Largest 4-digit number is 9999
Now, if we divide 9999 by 36, we will get 277.75 as quotient.
The integer just less than 277.75 is 277
∴ Required number = (36 × 277) + 4 = 9972 + 4 = 9976
Hence, the correct answer is option (a).