Answer: 4
Explanation:
AC is 15, so it can't be anything above 15 canceling out 15 and 36. That leaves us with 4 or 9.
Then try filling out m with one of the numbers we have. I tried 4 first:
4 × 4 - 15 = 1
5 × 4 - 6 = 14
Then add this.
1 + 14 = 15
This means that 4 is the answer because
AB & BC = AC