To simplify this fraction, first find the greatest common factor between them. The factors of 28 are [1, 2, 4, 7, 14, 28] and the factors of 60 are [1, 2, 3, 4, 5, 6, 10, 12, 15, 20, 30, 60]. They share 3 factors [1, 2, 4] making 4 their greatest common factor (GCF).

Next, divide both numerator and denominator by the GCF:

\( \frac{28}{60} \) = \( \frac{\frac{28}{4}}{\frac{60}{4}} \) = \( \frac{7}{15} \)

To divide terms with radicals, divide the coefficients and radicands separately:

\( \frac{20\sqrt{21}}{4\sqrt{7}} \)
\( \frac{20}{4} \) \( \sqrt{\frac{21}{7}} \)
5 \( \sqrt{3} \)

The least common multiple (LCM) is the smallest positive integer that is a multiple of two or more integers.

A factorial is the product of an integer and all the positive integers below it. To solve a fraction featuring factorials, expand the factorials and cancel out like numbers:

\( \frac{5!}{2!} \)
\( \frac{5 \times 4 \times 3 \times 2 \times 1}{2 \times 1} \)
\( \frac{5 \times 4 \times 3}{1} \)
\( 5 \times 4 \times 3 \)
60

To add 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:

\( \frac{6 x 3}{4 x 3} \) + \( \frac{6 x 2}{6 x 2} \)

\( \frac{18}{12} \) + \( \frac{12}{12} \)

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

\( \frac{18 + 12}{12} \) = \( \frac{30}{12} \) = 2\(\frac{1}{2}\)