\frac{20}{5 - \sqrt{5}}*\frac{5 + \sqrt{5}}{5 + \sqrt{5}} = \frac{100 + 20\sqrt{5}}{25 - 5} = \frac{100 + 20\sqrt{5}}{20} = 5 + \sqrt{5}
Now, compare (5 + \sqrt{5}) to (a + b\sqrt{5})
a = 5
b = 1
a+b = 5+1 = 6
Ans. B
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