Tính một cách hợp lý: a) x - (-7/9) = (-5/6) b) 15/-4 -x = 0,3

a)

$$\begin{gathered} x-\left(-\frac{7}{9}\right)=-\frac{5}{6} \\ x=-\frac{5}{6}+\left(-\frac{7}{9}\right) \\ x=-\left(\frac{5}{6}+\frac{7}{9}\right) \\ x=-\left(\frac{15}{18}+\frac{14}{18}\right) \\ x=-\frac{29}{18} \end{gathered}$$

Vậy $x=-\frac{29}{18}$

b) $\frac{15}{-4}-x=0,3$

$$\begin{gathered} x=\frac{15}{-4}-0,3 \\ x=-\frac{15}{4}-\frac{3}{10} \\ x=-\frac{75}{20}-\frac{6}{20} \\ x=-\left(\frac{75}{20}+\frac{6}{20}\right) \\ x=-\frac{81}{20} \\ \text{Vậy }x=-\frac{81}{20} \end{gathered}$$