Is it simple!

It's simple.. as we know $37*3=111$ And Any number containing multiple of three time $1$ is dividable by $111$ is also dividable by $37$ . And then given number divided by $37$ . Similarly $101*11=1111$ And any number containing multiple of four time $1$ Is dividable by $1111$ . So this number is also divided by botha $37$ And $101$ .

Every three digit number with same digit is divisible by 111 .and 300 is divisible by 3. So the number is divisible by 111.

To be frank, I just guessed.