12 is related to 16 following a certain logic. Following the same logic, 18 is related to 24. Which of the following numbers is related to 28 using the same logic?

The correct answer is 21.

Let us find the relationship between the numbers in the given pairs to determine the logical pattern.

First, let us analyze the first pair: 12 is related to 16.
If we look at the ratio of the two numbers:
$\frac{12}{16}=\frac{3}{4}$

Second, let us analyze the second pair: 18 is related to 24.
Similarly, checking the ratio of these two numbers:
$\frac{18}{24}=\frac{3}{4}$

The logic is that the ratio of the first number to the second number in each pair is consistently 3 : 4.
Or, expressed as an equation:
$\text{First Number}=\frac{3}{4}\times \text{Second Number}$

Now, we need to find the number that is related to 28 using the same logic. Here, 28 is the second number of the pair.
Let the required first number be $x$.
Using the established ratio of 3 : 4:
$\frac{x}{28}=\frac{3}{4}$

Solving for $x$:
$x=28\times \frac{3}{4}$
$x=7\times 3$
$x=21$

Therefore, the number related to 28 is 21.