The correct equation is m + 13 = a.
To solve this question, we need to figure out a pattern between the number of people attending in the morning and the number of people attending in the afternoon.
The first one:
37 - 24 = 13
Second one:
43 - 30 = 13
From this, we can see that our pattern is that the afternoon has 13 more people in attendance. Now we need to find the equation that shows that, and, like you circled, the correct answer is m + 13 = a.