The amount one person will pay for a day is $4 The amount two people will pay for a day is $8 The amount Beth paid for 3 days is 4*3=12 The amount Maria paid for 3days is also 4*3=12 So to find the amount they will pay for 3days, add 12 and 12 to get 24. The girls will pay $24 for the 3days.