According to me answer should be D........But don't know why it is wrong

Agreed with Sonalika. D it is

Are you certain that Quantity A is 12 + 15q not "12p + 15q".

If so then the answer is D.
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yes i am sure

Answer is D bcoz there is no necessary info. about the value of x and y.

Edited the OA.

regards
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Given: 4p + 5q = 7
Multiply both sides by 3 to get the EQUIVALENT equation: 12p + 15q = 21
Subtract 12p from both sides to get: 15q = 21 - 12p

Now onto the question!!
Quantity A: 12 + 15q
Quantity B: 20

Replace 15q with 21 - 12p to get:
Quantity A: 12 + (21 - 12p)
Quantity B: 20

Simplify to get:
Quantity A: 33 - 12p
Quantity B: 20

Subtract 33 from both sides to get:
Quantity A: -12p
Quantity B: -13

Let's test some values
If p = 0, then we get:
Quantity A: -12(0) = 0
Quantity B: -13
Quantity A is greater

If p = 2, then we get:
Quantity A: -12(2) = -24
Quantity B: -13
Quantity B is greater

Answer: D

Cheers,
Brent
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for obtaining 4p + 5q = 7, we can use both positive and negative values for P as well as q,Therefore answer should be D