HI

Firstly , graph this 4 first lines first .

take the area below this line , <

take the area above this line , >=

x=0 take area to the right of the line , >=

x=12 take are to the left of the line , <=

Then , the 'quadrilateral' as a result of the intersection of these lines is most likely to be the region bounded . I am not saying it's but normally it is . So now you will have to check .