Question 787926
for this one your going to have to use 2 equations,  you have 2 ticket prices that sold 500 total, so that equation will be

a  +  c  = 500

second equation, adult ticket prices were 11 dollars, and children prices were 6 dollars, for a total of 3900 dollars, so that equation will be...

11a + 6c = 3900

lets solve using elimination method

a  + c  = 500
11a + 6c =  3900

we want to get rid of one of our variables, so lets multiply the top line by -6

-6a - 6c  = -3000
11a + 6c  = 3900

lets add the two lines up thereby eliminating 6c

5a = 900

divide both sides by 5

a = 180

now that we know the value of a, we can plug that into our original equation to find out the value of c

11(180) + 6c = 3900

1980 + 6c = 3900

6c = 1920

c = 320

plug in both values to doublecheck their accuracy, but your total ticket sales are....

180 adult tickets, and 320 children tickets.