Vă rog! ! ! ! ! ! ! ! ! ! !

[tex]-\frac{3}{21} - [\frac{5}{42} - \frac{1}{14} - \frac{2}{21}]\\ = -\frac{3}{21} - [\frac{5-3-4}{42} \\= -\frac{3}{21} + \frac{2}{21} \\= \frac{5}{21}[/tex]