Because if you divide the number of month by 12, the duration of an year in months, you get 33.3 which means 33 exact years plus 0.3 years that is how to take 1/3 of a year (1/3 = 0.33).

Any number of months that is a multiple of 12 will take us to June again. Thus, we have 12, 24, 36, … that take us to June. Since 400/12 = 33 remainder 4, we see that in 33 x 12 = 396 months, it will be June, and 4 months after that it will be October.

Answer: D

If it is now June, what month will it be 400 months from now?

As we know that each year has 12 months. So the months will repeat after 12 months.

Month Now, or Month 1 from now = Month 13\(^{th}\) = Month 25\(^{th}\) = July
=> If we take remainder of the month number by 12 then the remainder month number and original month number will be same

Example. Remainder of 13 by 12 is 1 => Month 13 = Month 1

( Watch this video to learn about the Basics of Remainders )

=> Remainder of 400 by 12 is 4 => Month 400 = Month 4 = October

So, Answer will be D
Hope it helps!

Watch the following video to learn How to Sequence problems