in an ordinary day with no discount if u see the parretn you can get the cost per ticket by dividing the cost by number of tickets 1st : 21/3 =7 2nd: 35/5=7 3rd: 56/8 = 7 so the ticket in an ordinary day = $7 in friday they make discount by $2 so the new value of the ticket = the old value -2 so the ticket on friday = $5 so if you want 9 tickets 9*5 = $45