Answer:
283 people went this year to the stadium.
Explanation:
Let's put this data into pieces so it's less overwhelming.
Last year 260 students went to the prom.
Currently the number of students who attended has increased by 9% from last year.
And the question is asking how many students attended this year?
Well, if this is increasing by 9%, wouldn't we just find 9% of 260 then add it to 260?
0.09 * 260 = 23.4
260 + 23.4 = 283.40. Obviously we can't have 40% of a human being, so let's round it to 283.