By buying two shirts, Ezra will save $19 x \( \frac{15}{100} \) = \( \frac{$19 x 15}{100} \) = \( \frac{$285}{100} \) = $2.85 on the second shirt.

There are 4 3-passenger taxis available so that's 4 x 3 = 12 total seats. There are 16 people needing transportation leaving 16 - 12 = 4 who will have to find other transportation.

In order to find how many additional workers are needed to staff the extra crews you first need to calculate how many workers are on a crew. There are 10 workers at the company now and that's enough to staff 5 crews so there are \( \frac{10}{5} \) = 2 workers on a crew. 9 crews are needed for the busy season which, at 2 workers per crew, means that the roofing company will need 9 x 2 = 18 total workers to staff the crews during the busy season. The company already employs 10 workers so they need to add 18 - 10 = 8 new staff for the busy season.

To subtract these fractions, first find the lowest common multiple of their denominators. The first few multiples of 2 are [2, 4, 6, 8, 10, 12, 14, 16, 18, 20] and the first few multiples of 8 are [8, 16, 24, 32, 40, 48, 56, 64, 72, 80]. The first few multiples they share are [8, 16, 24, 32, 40] making 8 the smallest multiple 2 and 8 share.

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

\( \frac{5 x 4}{2 x 4} \) - \( \frac{3 x 1}{8 x 1} \)

\( \frac{20}{8} \) - \( \frac{3}{8} \)

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

\( \frac{20 - 3}{8} \) = \( \frac{17}{8} \) = 2\(\frac{1}{8}\)

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:

-8c⁴ + 1c⁴
(-8 + 1)c⁴
-7c⁴