"Quadruple" means, roughly, "multiply something by 4."
Quadruple (3/4) lb of onions = 4(3/4) lb of onions = 3 lb of onions.
Quadruple (1 1/3) lb of pork = 4(4/3) lb of pork = 16/3 lb of pork = 5 1/3 lb of pork.
