Help me with the top four questions please

I did these problems on my math class a few years ago

Number of children, x= 400

Number of adults, y = 100

Step-by-step explanation:

Let the number of children be x

Let the number of  adults be y

Given : Total number of people,  x + y = 500  (1)

           Total amount collected, 5x + 10y = 3000  (2)

(1) => y = 500 - x

Substitute y in (2) : 5x + 10(500 - x) = 3000

                             5x + 5000 - 10x = 3000

                                -5x = 3000 - 5000

                                 -5x = -2000

                                    x = 400

Substitute x in (1) : 400 + y = 500

                                      y = 500 - 400

                                      y = 100