Let x = the number of refrigerators
Let y = the number of upright pianos



We graph the boundary line:



Divide through by 25 to simplify:



The intercepts are  and 

We draw the boundary line, and shade below it because the
origin used as a test point:


 

gives a true inequality



Will 10 refrigerators and 9 pianos overload the truck?

The points inside or on the boundary of the shaded region
represent the loads the truck can carry.  The x-coodinate
is the number of refrigerators, and the y-coordinate is
the number of pianos.

We plot the point (10,9) and see if it is in the shaded region:



The point (10,9) is outside the shaded region, so yes,
10 refrigerators and 9 pianos will overload the truck.

Edwin