$18 tickets are being compared to vip tickets.
So let x = the number of vip tickets sold.
Then 10x = the number of $18 tickets sold.
Let y = the number of $21 tickets sold.
the number of $18 tickets sold was 57 more than the sum of the number of $21 and $40 tickets
The above translates to 10x = x+y +57
You can solve this for y. y = 9x - 57.
The total cost will then be ????? = $51,973