To find the average of these 4 numbers add them together then divide by 4:

\( \frac{13 + 11 + 15 + 9}{4} \) = \( \frac{48}{4} \) = 12

The distributive property for division helps in solving expressions like \({b + c \over a}\). It specifies that the result of dividing a fraction with multiple terms in the numerator and one term in the denominator can be obtained by dividing each term individually and then totaling the results: \({b + c \over a} = {b \over a} + {c \over a}\). For example, \({a^3 + 6a^2 \over a^2} = {a^3 \over a^2} + {6a^2 \over a^2} = a + 6\).

The equation for this sequence is:

a_n = a_n-1 + 3(n - 1)

where n is the term's order in the sequence, a_n is the value of the term, and a_n-1 is the value of the term before a_n. This makes the next number:

a₆ = a₅ + 3(6 - 1)
a₆ = 31 + 3(5)
a₆ = 46

To divide terms with radicals, divide the coefficients and radicands separately:

\( \frac{10\sqrt{16}}{5\sqrt{8}} \)
\( \frac{10}{5} \) \( \sqrt{\frac{16}{8}} \)
2 \( \sqrt{2} \)

There are 2 3-passenger taxis available so that's 2 x 3 = 6 total seats. There are 7 people needing transportation leaving 7 - 6 = 1 who will have to find other transportation.