Select the option that is related to the fifth number in the same way as the fourth number is related to the third number and the second number is related to the first number.$56:51::71:64::69:?$

Let's discover the relation between the pairs of numbers:Pair 1: $56:51\to 56-5=51$ Pair 2: $71:64\to 71-7=64$ Notice the value being subtracted:In 56, the first digit is 5, and we subtract 5.In 71, the first digit is 7, and we subtract 7.Pattern: $\text{Number}-(\text{First digit of the number})=\text{Result}$ Applying this to the third pair (69):The first digit of 69 is 6.$69-6=63$ Therefore, the missing number is 63.