Analyze the pattern: 7/2=3, 16/9=5, 21/5=8, 43/?

The first set has 7 and 2 at the top, and 3 at the bottom.
Let's try summing the top numbers and comparing it to the square of the bottom number:

$$7 + 2 = 9$$ $$3^2 = 9$$

The sum of the top numbers equals the square of the bottom number.

The second set has 16 and 9 at the top, and 5 at the bottom.
Let's apply the same pattern:

$$16 + 9 = 25$$ $$5^2 = 25$$

The pattern holds true for the second set.

The third set has 21 and 43 at the top, and 8 at the bottom.
Let's apply the same pattern:

$$21 + 43 = 64$$ $$8^2 = 64$$

The pattern holds true for the third set as well.

The pattern observed in "SAMPLE A" is that the sum of the two numbers in the top boxes is equal to the square of the number in the bottom box.

The pattern is: $\text{Sum of top numbers} = (\text{Bottom number})^2$.