To subtract these fractions, first find the lowest common multiple of their denominators. The first few multiples of 4 are [4, 8, 12, 16, 20, 24, 28, 32, 36, 40] and the first few multiples of 6 are [6, 12, 18, 24, 30, 36, 42, 48, 54, 60]. The first few multiples they share are [12, 24, 36, 48, 60] making 12 the smallest multiple 4 and 6 share.

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

\( \frac{7 x 3}{4 x 3} \) - \( \frac{8 x 2}{6 x 2} \)

\( \frac{21}{12} \) - \( \frac{16}{12} \)

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

\( \frac{21 - 16}{12} \) = \( \frac{5}{12} \) = \(\frac{5}{12}\)

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. 10 crews are needed for the busy season which, at 2 workers per crew, means that the roofing company will need 10 x 2 = 20 total workers to staff the crews during the busy season. The company already employs 10 workers so they need to add 20 - 10 = 10 new staff for the busy season.

The factors of 80 are [1, 2, 4, 5, 8, 10, 16, 20, 40, 80] and the factors of 68 are [1, 2, 4, 17, 34, 68]. They share 3 factors [1, 2, 4] making 4 the greatest factor 80 and 68 have in common.

The equation for this sequence is:

a_n = a_n-1 + 4

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 + 4
a₆ = 17 + 4
a₆ = 21

The yearly interest charged on this loan is the annual interest rate multiplied by the amount borrowed:

interest = annual interest rate x loan amount

i = (\( \frac{6}{100} \)) x $700
i = 0.06 x $700
i = $42