For the example problem of system of inequalities, you have to determine which combination of the number of speakers and the number of floodlights is in the solution set. 

There are actually many possible combinations that satisfy the system of inequalities, so substituting each answer choice one by one would be the best way.  

If you have to find a minimum of a variable or a maximum of a variable, then those values are always on intersection of two inequalities. In this case, you can find a solution by solving system of equations even if system of inequalities is given. 

Thank you for taking my class earnestly. 

Best regard, Liz