Question 4930
rewrite your problem: 
√9x^2/√18x^2=(√9)(√x^2)/(√18)(√x^2)
            =3x/3x√2 
            =3x(√2)/3x√2
            =√2

√9=3
√x^2=x
√18=√9x2=3√2 (not a perfect square, so factor out the 18)
multiply both sides by √2 and the 3x cancel out.

2√20 - 3√7 - 2√5 + 4√63 
= 2(√4)(√5) - 3√7 -2√5 + 4(√9)(√7) *√4=2, √9=3 
= (2)(2)√5 -3√7 - 2√5 + (4)(3)√7
= 4√5 - 3√7 - 2√5 + 12√7
(you can only add the same radicals together)
= 4√5 - 2√5 - 3√7 + 12√7
= 2√5 + 9√7
Yes! You were right.