7.4. Find the smallest natural number ending in the digit 6 (on the right) which, when this digit is moved to the beginning (to the left), increases exactly four times.
Solution. Multiplication "in column" is performed from the end, so we can start the process of multiplication by sequentially finding all the digits: *****6 ( $6 \times 4=24$ - "4 we write, 2 in mind" - the 4 written under the line is the 4th digit that stood before 6; by writing 4 in the top line before 6, we will continue the process until the 6 appears in the bottom line.

Answer: 153846.