Answer:
[tex]8\sqrt{7}[/tex]
Step-by-step explanation:
[tex]\frac{21}{\sqrt{7} } * \frac{\sqrt{7} }{\sqrt{7} }[/tex] = [tex]\frac{21\sqrt{7} }{7}[/tex]
[tex]\frac{21\sqrt{7} }{7}[/tex] = [tex]\frac{147\sqrt{7} }{14}[/tex]
[tex]\frac{147\sqrt{7} }{14} - \frac{35\sqrt{7} }{14}[/tex]
[tex]\frac{112\sqrt{7} }{14}[/tex]
[tex]8\sqrt{7}[/tex]
