Let \(c\) be the number of children; \(m\) be the number of men and \(w\) be the number of women
\(c + m + w = 316\)
\(c = 78 + w\)
\(w = 56 +m\)
\(78+56+m + 56+m +m = 316\)
\(190 +3m = 316\)
\(m = 42\)
Answer: There are 42 men watching a movie