(c) \(76\frac{2}{3}\)days
15 men’s 1 days’ work = \(\frac{1}{210}\)
\(\therefore\) 15 men’s 10 days’ work = \(\frac{10}{210}\) = \(\frac{1}{21}\)
Remaining work = 1 - \(\frac{1}{21}\) = \(\frac{20}{21}\)
The additional 15 men’s 1 days’ work = \(\frac{2}{210}\) = \(\frac{1}{105}\)
\(\therefore\) These 30 men’s 1 days’ work = \(\big(\frac{1}{210}+\frac{1}{105}\big)\) = \(\frac{1+2}{210}\) = \(\frac{3}{210}\) = \(\frac{1}{70}\)
\(\frac{1}{70}\)th of the work can be done in 1 day
\(\therefore\) \(\frac{20}{21}\)th of the work can be done in \(\big(70\times\frac{20}{21}\big)\)days = \(\frac{200}{3}\)days = 66\(\frac{2}{3}\)days
\(\therefore\) Total no. of days = 66\(\frac{2}{3}\)days + 10 days = \(76\frac{2}{3}\)days
