Let's break this down step by step:

(х- 3 целых 13/21) + 2 целых 10/21

First, we add the whole numbers together: -3 + 2 = -1

Now, we add the fractions together: 13/21 + 10/21 = 23/21

So, the expression simplifies to:

x - 1 целых 23/21

To convert this to a mixed number, we divide 23 by 21:

23 ÷ 21 = 1 целых 2/21

Therefore, the final answer is:

x - 1 целых 2/21