Let the number of bottled water be x and number of medical kits be y.
It is given that the bottled water weighs 20 pounds per container and measures 1 cubic foot and the medical kits each weigh 10 pounds and measure 2 cubic feet.
Also the plane can carry 90000 pounds so it follows:
The plane can carry 6000 cubic feet so it follows:
Multiply equation (i) by -2 to get:
Add (ii) and (iii) to get:
Substitute the value x=4000 in (i) to get:
Hence each plane can carry 4000 bottled water and 1000 medical kits.