12 men : 8 hours : 10 days
// Find if every man works 1 hour
12 x 8 men : 1 hour : 10 days
96 men : 1 hour : 10 days
//Find if every man works 15 hours
96 ÷ 15 men : 15 hours : 10 days
6.4 men : 15 hours : 10 days
//Find if every man works 1 day
6.4 x 10 men : 15 hours : 1 day
64 men : 15 hours : 1 day
//Find if every man works 8 days
64 ÷ 8 men : 15 hours : 8 days
8 men : 15 hours : 8 days
Answer: 8 men is needed