Approximation and quick calculation: Evaluate 3.2 × 8.1 + (3185 ÷ 4.95) and select the closest option.

Introduction / Context:
The division term dominates. Approximating 4.95 as 5 gives a baseline, and a small upward correction (because the actual divisor is slightly less than 5) refines it enough to select the nearest ten-level option.

Given Data / Assumptions:

• Main term: 3185 / 4.95
• Small term: 3.2 * 8.1

Concept / Approach:
First compute 3185/5 = 637. Then adjust upward because dividing by 4.95 (smaller divisor) yields a slightly larger quotient. Add the small product 3.2*8.1 ≈ 25.92 to reach the final estimate near 670.

Step-by-Step Solution:

Verification / Alternative check:
Exact computation gives about 669.35; among the choices 660, 645, 690, the closest is 670 by less than 1.

Why Other Options Are Wrong:
660 and 645 are too low; 690 is too high. 670 is nearly exact.

Common Pitfalls:
Forgetting to add the product term or using 3185/5 without the correction for the slightly smaller divisor 4.95.

Final Answer:
670