For this problem, let x be the number of children and y for adults. Formulate the equations: 1st equation, x + y = 3,200 and 2nd equation 5x + 9y = 24,000. Re-arrange 1st equation into x = 3200 - y. Then, substitute into 2nd equation, 5(3,200-y) + 9y = 24,000. Then, solve for y. The 16,000 - 5y + 9y = 24000. Final answer is, y = 2000 adults went to watch the movie.
the scale factor or ratio of two similar figures, will be the same as the ratio of their perimeter, or even the ratio of two corresponding sides.
for example, we have say, an irregular octagon with a perimeter of say 13, and a similar octagon with a perimeter of 39, then

which is another way to say, the smaller is 1/3 of the larger one, or the larger one is 3 times as the smaller one.
-3.375 or -3.4 or -3.38 all the same answer