5. Решите уравнение: a) (a + 3 2/17) - 12/51 = 3 2/3 b) 1 7/18 + (4 21/45 - t) = 5 6/15

а) $$(a + 3 \frac{2}{17}) - \frac{12}{51} = 3 \frac{2}{3}$$ $$a + 3 \frac{2}{17} = 3 \frac{2}{3} + \frac{12}{51}$$ $$a + 3 \frac{2}{17} = 3 \frac{34}{51} + \frac{12}{51}$$ $$a + 3 \frac{2}{17} = 3 \frac{46}{51}$$ $$a = 3 \frac{46}{51} - 3 \frac{2}{17}$$ $$a = 3 \frac{46}{51} - 3 \frac{6}{51}$$ $$a = \frac{40}{51}$$

б) $$1 \frac{7}{18} + (4 \frac{21}{45} - t) = 5 \frac{6}{15}$$ $$4 \frac{21}{45} - t = 5 \frac{6}{15} - 1 \frac{7}{18}$$ $$4 \frac{7}{15} - t = 5 \frac{2}{5} - 1 \frac{7}{18}$$ $$4 \frac{7}{15} - t = 4 \frac{2}{5} - \frac{7}{18}$$ $$4 \frac{7}{15} - t = 4 \frac{36}{90} - \frac{35}{90}$$ $$4 \frac{7}{15} - t = 4 \frac{1}{90}$$ $$t = 4 \frac{7}{15} - 4 \frac{1}{90}$$ $$t = \frac{42}{90} - \frac{1}{90}$$ $$t = \frac{41}{90}$$

Ответ: а) $$a = \frac{40}{51}$$; б) $$t = \frac{41}{90}$$