Решение:
12\(\frac{3}{17}\) = \(\frac{12 \times 17 + 3}{17}\) = \(\frac{204 + 3}{17}\) = \(\frac{207}{17}\)
8\(\frac{16}{17}\) = \(\frac{8 \times 17 + 16}{17}\) = \(\frac{136 + 16}{17}\) = \(\frac{152}{17}\)
23\(\frac{2}{17}\) = \(\frac{23 \times 17 + 2}{17}\) = \(\frac{391 + 2}{17}\) = \(\frac{393}{17}\)
\(\frac{207}{17}\) + x + \(\frac{152}{17}\) = \(\frac{393}{17}\)
\(\frac{207 + 152}{17}\) + x = \(\frac{393}{17}\)
\(\frac{359}{17}\) + x = \(\frac{393}{17}\)
x = \(\frac{393}{17}\) - \(\frac{359}{17}\)
x = \(\frac{393 - 359}{17}\)
x = \(\frac{34}{17}\)
x = 2
Ответ: 2