Question 22948
Because you have four lines to work with, graph all of 
the four inequalities on a fairly large sheet of paper.
You should end up with an enclosed area with four vertices
where the various pairs of edges meet.
For example, one of these vertices is (0,-6) where y>=x-7
and y= x+1 meet.
After you find the coordinates of these four points, put
their respective (x,y) values into the equation f(x,y)
= 6x+11y.
The minimum and the maximum value is what you are asked to find.

Cheers,
Stan H.