To solve this equation, we will follow the order of operations (PEMDAS).

First, let's simplify the terms inside the parentheses:

3 15/28 = (3 28 + 15) / 28 = 87 / 28
9/28 = 9 / 28
1 10/49 = (1 49 + 10) / 49 = 59 / 49

Now, we can substitute these values back into the equation:

21 2/59 - 2/5 * (87/28 : 9/28 - 1 : 59/49) : 2

Next, let's simplify the division inside the parentheses:

87/28 ÷ 9/28 = (87/28) (28/9) = 87/9 = 29
1 ÷ 59/49 = 1 49/59 = 49/59

Now, substitute these values back into the equation:

21 2/59 - 2/5 (29 - 1 : 49/59) : 2
21 2/59 - 2/5 (29 - 49/59) : 2

Now, let's simplify inside the parentheses:

29 - 49/59 = (29 * 59 - 49) / 59 = 1711 / 59

Substitute back into the equation:

21 2/59 - 2/5 (1711/59) : 2
21 2/59 - 2/5 1711/59 : 2
21 2/59 - 3422/295 : 2

Now, let's simplify the division:

3422/295 ÷ 2 = (3422/295) * (295/2) = 3422/590 = 1711/295

Substitute back into the equation:

21 2/59 - 1711/295 : 2
21 2/59 - 1711/295 / 2
21 2/59 - 1711/295 * 1 / 2
21 2/59 - 1711/590
21 2/59 - 5 421/590
15 151/59 - 5 421/590

Now, let's find a common denominator to subtract these fractions:

(denominator = 59 * 590)

(15 590 59 + 151 590) / (59 590) - (5 59 590 + 421 59) / (59 590)
(8850 + 89090) / (59 590) - (2950 + 24839) / (59 590)
(97940) / (59 590) - (27789) / (59 590)
(97940 - 27789) / (59 * 590)
70151 / 34,810

Therefore, the final answer is 70151 / 34,810.