To simplify this all you need to do is distribute the 4x across each term in the parenthesis
18 choose 7
=C(18,7)
=18!/(7!(18-7)!)
=31824
OR
18 choices for first passenger,
17 choices for second passenger,
....
12 choices for 7th passenger,
so total = 18*17*16...12
but there are 7! ways to order the 7 passengers, so
number of groups
=18*17*16...12/7!
=31824 as well
2yards= 72 inches
72 inches= 6 feet
so now that you know that, you know that she needs 6 feet and already has 3 feet. so she just needs 3 feet more. but they are asking for the answer to be in inches.
3 feet= 36 inches
your answer in 36 inches
She fill 12 bags because if you take 3/4*11 3/8- 1/8=12
