A rational number (or fraction) is represented as a ratio between two integers, a and b, and has the form \({a \over b}\) where a is the numerator and b is the denominator. An improper fraction (\({5 \over 3} \)) has a numerator with a greater absolute value than the denominator and can be converted into a mixed number (\(1 {2 \over 3} \)) which has a whole number part and a fractional part.

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 12 workers at the company now and that's enough to staff 4 crews so there are \( \frac{12}{4} \) = 3 workers on a crew. 7 crews are needed for the busy season which, at 3 workers per crew, means that the roofing company will need 7 x 3 = 21 total workers to staff the crews during the busy season. The company already employs 12 workers so they need to add 21 - 12 = 9 new staff for the busy season.

A ratio of 4:1 means that there are 4 home fans for every one visiting fan. So, of every 5 fans, 4 are home fans and \( \frac{4}{5} \) of every fan in the stadium is a home fan:

39,000 fans x \( \frac{4}{5} \) = \( \frac{156000}{5} \) = 31,200 fans.

To add 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 14 are [14, 28, 42, 56, 70, 84, 98]. The first few multiples they share are [42, 84] making 42 the smallest multiple 6 and 14 share.

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

\( \frac{2 x 7}{6 x 7} \) + \( \frac{8 x 3}{14 x 3} \)

\( \frac{14}{42} \) + \( \frac{24}{42} \)

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

\( \frac{14 + 24}{42} \) = \( \frac{38}{42} \) = \(\frac{19}{21}\)

To convert a negative exponent to a positive exponent, calculate the positive exponent then take the reciprocal.