Question 29889
I am assuming that the 5 is being multiplied by the root, and we are not looing for the 5th root here.
{{{ 5(sqrt(75x^3)) + sqrt(3x) }}} work {{{ sqrt(75x^3) }}} first
{{{ sqrt(75x^3) }}} 
{{{ sqrt(5*5*3*x*x*x) }}} taking pieces out in pairs ...
{{{ (5x)(sqrt(3x)) }}}
{{{ 5(5x)(sqrt(3x)) + 1(sqrt(3x)) }}} multiply
{{{ 25x(sqrt(3x)) + 1(sqrt(3x)) }}} add
{{{ 26x(sqrt(3x)) }}}