a) $$3\frac{4}{15} + y = 7\frac{11}{15}$$
$$y = 7\frac{11}{15} - 3\frac{4}{15}$$
$$y = (7-3) + (\frac{11}{15} - \frac{4}{15})$$
$$y = 4 + \frac{11-4}{15}$$
$$y = 4 + \frac{7}{15} = 4\frac{7}{15}$$
б) $$5\frac{4}{13} - x = 4\frac{5}{13}$$
$$x = 5\frac{4}{13} - 4\frac{5}{13}$$
$$x = 5 + \frac{4}{13} - 4 - \frac{5}{13}$$
$$x = (5-4) + (\frac{4}{13} - \frac{5}{13})$$
$$x = 1 - \frac{1}{13} = \frac{13}{13} - \frac{1}{13} = \frac{12}{13}$$
Ответ: a) $$y = \bf{4\frac{7}{15}}$$, б) $$x = \bf{\frac{12}{13}}$$