Question 342488
Not sure what the lower - in front of the 21 and 4 is. But let's say it is an equal sign (as opposed to a negative)
{{{6x+9 >=21}}} subtract 9 from both sides
{{{6x >= 12}}} divide both sides by 6
{{{x >= 2}}}
Here is a plot
http://www.wolframalpha.com/input/?i=6x%2B9+%3E+21

Same idea for the other one