The four-digit number 34☐6 is divisible by 9. What digit goes in the box?

Explanation

1. 01

   A number is divisible by 9 when its digit sum is a multiple of 9.

2. 02

   $3 + 4 + 6 = 13$, and the next multiple of 9 is 18.

3. 03

   So the missing digit is $18 - 13 = 5$.