1/2 cup of salt corresponds to 1/4 cup of pepper, 1/8 cup of garlic powder, and 1/8 cup of onion powder.
Batch 1
To find the equivalent measures to 1 cup of salt, we can use the next proportions:

Solving for x,


The amount of onion powder is also 1/4 cup
Batch 2
To find the equivalent measures to 1 cup of pepper, we can use the next proportions:


The amount of onion powder is also 1/2 cup
Batch 3
To find the equivalent measures to 1 cup of garlic powder, we can use the next proportions:



Part B
One half of the 12 cups of the mixture is salt, one fourth is pepper and one eighth is garlic powder and onion powder. That is,
Salt: 12*1/2 = 6
Pepper: 12*1/4 = 3
Garlic powder: 12*1/8 = 3/2
Onion powder: 12*1/8 = 3/2