64.
The answer is: B
Explanation
The relationship between the numbers on the left-hand side and right-hand side of the ratio sign is the same. Therefore, we can use the same relationship to find the missing value.
To find the missing value, we can cross-multiply the ratio and solve for the unknown value.
That is,
63/21 = 27/x
Cross-multiplying:
63x = 21 * 27
63x = 567
Dividing both sides by 63:
x = 9
Therefore, the missing value is 9.
So, 63:21 :: 27:9.