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:

-5a³ + 4a³
(-5 + 4)a³
-a³

The first few multiples of 3 are [3, 6, 9, 12, 15, 18, 21, 24, 27, 30] and the first few multiples of 5 are [5, 10, 15, 20, 25, 30, 35, 40, 45, 50]. The first few multiples they share are [15, 30, 45, 60, 75] making 15 the smallest multiple 3 and 5 have in common.

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. 8 crews are needed for the busy season which, at 2 workers per crew, means that the roofing company will need 8 x 2 = 16 total workers to staff the crews during the busy season. The company already employs 10 workers so they need to add 16 - 10 = 6 new staff for the busy season.

By buying two shirts, Charlie will save $21 x \( \frac{25}{100} \) = \( \frac{$21 x 25}{100} \) = \( \frac{$525}{100} \) = $5.25 on the second shirt.

So, his total cost will be
$21.00 + ($21.00 - $5.25)
$21.00 + $15.75
$36.75

A factor is a positive integer that divides evenly into a given number. For example, the factors of 8 are 1, 2, 4, and 8.