How much will be decreased to each terms of ratio 16 : 19, so that it will be 7 : 6?

Answer: Option A

Let, each term be 16a and 19a, and the number subtracted from it is x.
$$\frac{16a-x}{19a-x}=\frac{7}{6}$$
⇒ 96a - 6x = 133a - 7x
⇒ x = 133a - 96a
⇒ x = 37a
Hence, the number will be the multiple of 37.
So, from option A is a right answer.