Both x and y vary directly with each other and when x is 10, y is 14, which of the following is not a possible pair of corresponding values of x and y?
Both x and y vary directly with each other.
i.e. x 
if x = 10 and y = 14
so, 10  14 or 5
 14 or 5  7
7
This proportion is not follow in option (b) pairs.
Hence, Option(b) is correct.