[tex]7\sqrt{32}-6\sqrt{72}=7\sqrt{16\cdot2}-6\sqrt{36\cdot2}\\\\=7\cdot\sqrt{16}\cdot\sqrt2-6\cdot\sqrt{36}\cdot\sqrt2\\\\=7\cdot4\cdot\sqrt2-6\cdot6\cdot\sqrt2=28\sqrt2-36\sqrt2\\\\=-8\sqrt2[/tex]
[tex]Used:\\\\\sqrt{a\cdot b}=\sqrt{a}\cdot\sqrt{b}[/tex]
