Cho a,b,c thõa mãn \sqrt{a}+\sqrt{b}+\sqrt{c}=7;a+b+c=23;\sqrt{abc}=3.Tính gt bt H=\frac{1}{\sqrt{ab}+\sqrt{c}-6}+\frac{1}{\sqrt{bc}+\sqrt{a}-6}+\frac{1}{\sqrt{ca}+\sqrt{b}-6}