Question 712446
Square both sides and simplify.  Square again both sides and simplify again.  


The situation you were given is based on having summable irrational numbers, so you can't simply bring them together as factors.  


{{{ sqrt (b)-6=-2* sqrt(b) }}}
b-12*sqrt(b)+36=4*b
{{{-12*sqrt(b)=4b-36-b}}}
{{{12*sqrt(b)=b-4b+36}}}
{{{12*sqrt(b)=36-3b}}}
{{{12*sqrt(b)=3(12-b)}}}
{{{4*sqrt(b)=12-b}}}


{{{16*b=144-24b+b^2}}}
{{{highlight(b^2-40b+144=0)}}}

Using general solution to quadratic formula, to avoid looking for factoring the trinomial, b=4 or b=36; but you should test to see if both of these will work in the original equation.