Question 281085
As a general rule, I can say that
{{{sqrt(a*b^c) = sqrt(a)*b^(c/2)}}}
Suppose the problem was
{{{4b^4}}}
The square root is
{{{2b^2}}} since( {{{2*b*b}}})x({{{2*b*b}}}) = {{{4b^4}}}
Your problem is 
{{{sqrt(64b^48)}}}
{{{sqrt(64) = 8}}}
{{{sqrt(b^48) = b^24}}}, so
{{{sqrt(64b^48) = 8b^24}}}