Of $28$ people in a park, $12$ are children and the rest are adults. $8$ people have to leave at $3$ pm; the rest do not. If, after $3$ pm, there are $6$ children still in the park, how many adults are still in the park ?

Use a double-set matrix to solve this problem. First, fill in the numbers given in the problem: $28$ total people in the park, $12$ children and the rest $(16)$ adults; $8$ leave at $3$ pm and the rest $(20)$ stay.Then, you are told that there are $6$ children left in the park after $3$ pm. Since you know there are a total of $20$ people in the park after $3$ pm, the remaining $14$ people must be adults.

Children Adults Total

Leave at $3$ $8$

Stay $6$ $14$ $20$

Total $12$ $16$ $28$ (option A)