Work do one = 5/21
Remaining work = 1- (5/2) = 16/21
5/21 of a work can be done in 6 days working
10 hours a day by = 10 m
1 work can be done in 6 days working 10 hours a day by = (10 × 21)/5
1 work can be done in 1 day working 10 hours day by = (10 × 21 × 6)/5 men
16/21 work can be done in 8 days working 10 hours a day by = (10 × 21 × 6 × 16)/(5 × 21 × 8) = 24 men