It's quite easy actually. Just get all the numbers that are less than 12 and make it a fraction over the maximum number, and in this scenario it's 100. So your end result is <u>11/100</u>
Let x tickets sold be adults, then (1024-x) were of childrens tickets, 9x+(1024-x)4 = 7680. The above equation is for total money solve it you will get x=720 hence, number of adult tickets were 720 and number of child tickets were 300 :)