Find the correctly matched pair: In each pair A–B, the second number should be the square root of the first number (i.e., B = sqrt(A)). Select the pair that satisfies this relation.

Introduction / Context:
This classification item asks you to recognize the correct functional mapping between two numbers in a pair. The mapping is B = sqrt(A). Exactly one option follows this rule; the rest are distractors.

Given Data / Assumptions:

• Pairs to test: 42–4, 36–6, 32–2, 15–5.
• All square roots considered are principal (non-negative) roots.

Concept / Approach:
If B = sqrt(A), then A must be a perfect square of B. Equivalently, A = B^2. We can check faster by squaring B and comparing to A.

Step-by-Step Solution:

Verification / Alternative check:
Take sqrt(A) directly. sqrt(36) = 6 (integer). For 42, 32, and 15, the square roots are not integers matching the listed B values. Hence only 36–6 works.

Why Other Options Are Wrong:

Common Pitfalls:
Confusing square roots with other operations (like halving) or assuming near-perfect squares qualify. Only exact perfect squares satisfy the relation.

Final Answer:
36 - 6 is the only correctly matched pair.