Final answer:
By setting up and solving a simple algebraic equation to represent the given information about the number of children and adults in the theater, we find that there are 105 children watching the movie.
Step-by-step explanation:
The subject of this question is mathematics, specifically the area that deals with basic algebra or simultaneous equations. Given that there are 140 people in a theater, and the number of children is three times the number of adults, we can solve this by setting up an equation. Let the number of adults be A and the number of children be C. The problem states two things: C = 3A, and the total number of people is A + C = 140.
We can substitute the first equation into the second to find the number of adults: A + 3A = 140. Simplifying this gives 4A = 140; therefore, A = 140 / 4 = 35. Then, using the first equation to find the number of children: C = 3 × 35 = 105 children. Hence, there are 105 children watching the movie.