The sum of it's digits is 5 times the hundreds digit, which means it must be 15 because 3 has to be the hundreds. Subtract 3 from 15 to get 12, the sum of the other two digits. Both digits must be odd and must be single digits. The number 3 cannot show up in the 2 digits because 3 is already in the hundreds place. That leaves one pair- 5 and 7. It must be 357 because the number must fit between 301 and 370
