Explanation

Its given that the number must be sum of 3 consecutive odd numbers. Then the numbers must be around 1/3 the original number

1) 15 So \(\frac{15}{3}\) =5, so the three consecutive odd numbers \(3+5+7 =15\)
2) 75 So \(\frac{75}{3}\) =25, so the three consecutive odd numbers \(23+25+27 =75\)
3) 123 So \(\frac{123}{3}\) =41, so the three consecutive odd numbers \(39+41+43 =123\)
4) 297 So \(\frac{297}{3}\) =99, so the three consecutive odd numbers \(97+99+101 =297\)
5) 313 Must be correct!