$a\text{)}3\sqrt{50}-2\sqrt{18}=3\sqrt{25\cdot 2}-2\sqrt{9\cdot 2}=3\sqrt{25}\cdot \sqrt{2}-2\sqrt{9}\cdot \sqrt{2}=3\cdot 5\sqrt{2}-2\cdot 3\sqrt{2}=15\sqrt{2}-6\sqrt{2}=9\sqrt{2}$    

$b\text{)}3\sqrt{8}-7\sqrt{2}=6\sqrt{2}-7\sqrt{2}=-\sqrt{2}$  

$c\text{)}6\sqrt{45}-3\sqrt{5}=18\sqrt{5}-3\sqrt{5}=15\sqrt{5}$  

$d\text{)}\sqrt{28}+2\sqrt{63}=2\sqrt{7}+6\sqrt{7}=8\sqrt{7}$  

$e\text{)}10\sqrt{13}-\sqrt{52}=10\sqrt{13}-\sqrt{4\cdot 13}=10\sqrt{13}-2\sqrt{13}=8\sqrt{13}$  

$f\text{)}-5\sqrt{98}-3\sqrt{18}=-5\cdot 7\sqrt{2}-3\cdot 3\sqrt{2}=-35\sqrt{2}-9\sqrt{2}=-44\sqrt{2}$  

$g\text{)}8\sqrt{20}-5\sqrt{80}=16\sqrt{5}-20\sqrt{5}=-4\sqrt{5}$