Using HCF × LCM = a × b:
$$\text{LCM}(2520, 6600) = \frac{2520 \times 6600}{40} = \frac{16632000}{40} = 415800$$
Given LCM = 252 × k, so $k = \dfrac{415800}{252} = \mathbf{1650}$.
Answer: A) 1650
The key property used is: HCF(a, b) × LCM(a, b) = a × b. First find LCM by dividing the product of the two numbers by their HCF, then divide LCM by 252 to get k. Examiners expect the formula to be stated and calculation shown step-by-step.