10 4/21 - (4 10/21 + 3 19/21)

First, let's add the two mixed numbers inside the parentheses:

4 10/21 + 3 19/21
= (4 + 3) + (10/21 + 19/21)
= 7 + 29/21
= 7 8/21
= 7 2/3

Now, we have:

10 4/21 - 7 2/3

Next, convert the mixed numbers to improper fractions:

10 4/21 = (10 x 21 + 4) / 21 = 214/21
7 2/3 = (7 x 3 + 2) / 3 = 23/3

Now, subtract the fractions:

214/21 - 23/3
= (214 x 3 - 23 x 21) / (21 x 3)
= (642 - 483) / 63
= 159 / 63
= 53 / 21

Finally, convert the improper fraction back to a mixed number:

53 / 21 = 2 11/21

Therefore, the solution is:

10 4/21 - (4 10/21 + 3 19/21) = 2 11/21