["Find total units: 11 + 2 = 13 units. Each unit = 390 / 13 = 30 passengers.","Economy = 11 x 30 = 330. Checked:didn't check = 4:1 so didn't check (economy) = 1/5 x 330 = 66.","Business = 2 x 30 = 60. Checked:didn't check = 9:1 so didn't check (business) = 1/10 x 60 = 6. Total = 66 + 6 = 72."]