There are 3 4-passenger taxis available so that's 3 x 4 = 12 total seats. There are 15 people needing transportation leaving 15 - 12 = 3 who will have to find other transportation.

To take the square root of a fraction, break the fraction into two separate roots then calculate the square root of the numerator and denominator separately:

\( \sqrt{\frac{36}{81}} \)
\( \frac{\sqrt{36}}{\sqrt{81}} \)
\( \frac{\sqrt{6^2}}{\sqrt{9^2}} \)
\(\frac{2}{3}\)

To multiply fractions, multiply the numerators together and then multiply the denominators together:

\( \frac{1}{8} \) x \( \frac{4}{6} \) = \( \frac{1 x 4}{8 x 6} \) = \( \frac{4}{48} \) = \(\frac{1}{12}\)

To subtract these fractions, first find the lowest common multiple of their denominators. The first few multiples of 6 are [6, 12, 18, 24, 30, 36, 42, 48, 54, 60] and the first few multiples of 10 are [10, 20, 30, 40, 50, 60, 70, 80, 90]. The first few multiples they share are [30, 60, 90] making 30 the smallest multiple 6 and 10 share.

Next, convert the fractions so each denominator equals the lowest common multiple:

\( \frac{6 x 5}{6 x 5} \) - \( \frac{9 x 3}{10 x 3} \)

\( \frac{30}{30} \) - \( \frac{27}{30} \)

Now, because the fractions share a common denominator, you can subtract them:

\( \frac{30 - 27}{30} \) = \( \frac{3}{30} \) = \(\frac{1}{10}\)

To add or subtract terms with exponents, both the base and the exponent must be the same. In this case they are so add the coefficients and retain the base and exponent:

6a² + 9a²
(6 + 9)a²
15a²