The answer is on the picture below
Answer:
n * 2 - 3
Step-by-step explanation:
Let's say n is the number of minutes Mike ran then the expression would be
n * 2 - 3
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
Algebra
The graph is C, or the graph down left.
This is because the other graphs lack the same vertex.