Regardless the initial price the discount in A is 50 and B is 75

B is greater

That's not quite right.
Paying $80 for a $100 shirt means a discount of $20
Paying $70 for a $100 shirt means a discount of $30
Total discount = $50

Total amount we would have paid WITHOUT the discount = $200
So, the total discount of $50, represents a discount of 25% (since $50/$200 = 25%)

Buying a shirt at 80% of the tagged price represents a 20% discount.
Buying a shirt at 70% of the tagged price represents a 30% discount.

The total percent discount for both shirts (Quantity A) depends on the tagged prices of the 2 shirts.

Let's look at 2 EXTREME cases:


case i: The first shirt (with the 20% discount) has a tagged price of $100, and the second shirt (with a 30% discount) has a tagged price of $1.
On the first shirt, we get a $20.00 discount.
On the second shirt, we get a $0.30 discount.
TOTAL discount = $20.30
TOTAL tag price = $101
TOTAL percent discount = $20.30/$101 ≈ 20.099%

case ii: The first shirt (with the 20% discount) has a tagged price of $1, and the second shirt (with a 30% discount) has a tagged price of $100.
On the first shirt, we get a $0.20 discount.
On the second shirt, we get a $30.00 discount.
TOTAL discount = $30.20
TOTAL tag price = $101
TOTAL percent discount = $30.20/$101 ≈ 29.90%

As we can see, if the first shirt (with the 20% discount) cost significantly more then the second shirt (with the 30% discount), then the total percent discount will be closer to 20%.
Conversely, if the second shirt (with the 30% discount) cost significantly more then the first shirt (with the 20% discount), then the total percent discount will be closer to 30%.

As we can see, the total percent discount will always be between 20% and 30%

In other words:
QUANTITY A: Some value between 20% and 30%
QUANTITY B: 75%

Answer: B

Cheers,
Brent

The total percent discount offered to John on the purchase of the two shirts is 75%.

So, the answer is (C) The two quantities are equal.