Question 107484
If {{{21/(15-3x)<0}}}
then (15-3x)<0 since the numerator is positive. 
{{{15-3x<0}}}
{{{15-3x+3x<3x}}}Add 3x to both sides.
{{{15<3x}}}
{{{15/3<3x/3}}}Divide both sides by 3.
{{{5<x}}} or
{{{x>5}}}
Check your answer. 
Pick a number greater than 5. Let's pick 10. 
The inequality should hold true since 10>5.
{{{21/(15-3x)<0}}}
{{{21/(15-3(10))<0}}}
{{{21/(15-30)<0}}}
{{{-21/15<0}}}
True statement. Good answer.
a. (5, &#8734;)