Answer:
c) x11 + x12 = 8000
Step-by-step explanation:
Xij = Gallons of the ith component used in the  jth Gasoline type
This invariably  tells us what component is in which gasoline type.
The gasoline types are:
Gasoline  1  = 11,000 gallons
Gasoline 2 = 14,000 gallons
Assuming two(2) components types:
Component 1
Component 2
The possible combinations Xij are :
             Gasoline 1           Gasoline 2
Component 1 Â Â Â Â Â X11 Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â X12
     Â
Component 2 Â Â Â Â X21 Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â X22
From the above , it is clear that the supply constraint for component 1 across the gasoline types is given by   X11  &  X12
Mathematically, since there are 8,000 gallons of Component 1, the supply constraint is given by:
X11 + X12 = 8000