[tex]\it AB||YZ\ \stackrel{T.f.a.}{\Longrightarrow}\ \Delta XYZ\sim\Delta XAB \Rightarrow \dfrac{YZ}{AB}=\dfrac{XY}{XA} \Rightarrow\dfrac{YZ}{6}=\dfrac{\dfrac{70}{6}}{7} \Rightarrow\\ \\ \\ \Rightarrow\ YZ=\dfrac{6\cdot\dfrac{70}{6}}{7}=\dfrac{70}{7}=10\ cm[/tex]
