"The digit at tens place is four times the digit at units place."
How many possible numbers are there?
1 in the units place: 41
2 in the units place: 82
If you try 3 in the units place, 4 * 3 = 12, you'd get 123, and now it's a three-digit number, so the only possibilities are 41 and 82.
41 or 82
If you subtract 54 from 41, you get a negative number, so 41 cannot be the number.
82 - 54 = 28, which has the digits of 82 in reverse order.
Answer: 82
