Theo đầu bài ta có:
\(\frac{x-7}{7}+\frac{x-7}{8}=\frac{15}{56}\)
\(\Rightarrow\left(x-7\right)\cdot\frac{1}{7}+\left(x-7\right)\cdot\frac{1}{8}=\frac{15}{56}\)
\(\Rightarrow\left(x-7\right)\cdot\left(\frac{1}{7}+\frac{1}{8}\right)=\frac{15}{56}\)
\(\Rightarrow\left(x-7\right)\cdot\frac{15}{56}=\frac{15}{56}\)
\(\Rightarrow x-7=1\)
\(\Rightarrow x=8\)