The answer is 457.
Start with the smallest number (4) then the large number (5) the the largest number (7).
The last digit must be an odd number if it is an even number switch the ones and tens.
If you want the SMALLEST ___ digit number then use this simple trick just write the given numbers in ASCENDING order , and if you want the LARGEST ___digit number just do the opposite.
It's quite easy if you understand it.
The smallest 3-digit odd number that can be made from 745 is 457. In writing the smallest 3-digit odd number, always start with the smallest digit then end with the highest digit then look if the last number is odd. If it is even, switch the tens and ones place.