Correct Answer: Option A

Explanation

The statement "P is partly constant and varies partly as Q" means P consists of a constant term plus a term directly proportional to Q. Thus, the relationship is:

P = a + bQ, where a is the constant part and b is the constant of proportionality.

Given:  
P = 32 when Q = 16 → a + 16b = 32  
P = 20 when Q = 12 → a + 12b = 20  

Subtract the second equation from the first:  
(a + 16b) - (a + 12b) = 32 - 20  
4b = 12  
b = 3  

Substitute b = 3 into the second equation:  
a + 12(3) = 20  
a + 36 = 20  
a = -16  

Thus, P = -16 + 3Q  

When Q = 28:   P = -16 + 3(28) = -16 + 84 = 68

There is an explanation video available below.

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