The greatest number, which divides 943 and 1957 to leave 7 and 1 respectively as remainders, is:

Correct option is A

Given:
The greatest number, which divides 943 and 1957 to leave 7 and 1 respectively
Solution:
The number which divides 943 and leaves remainder = 7
(943 - 7) = 936 is completely divisible by that greatest number
The number which divides 1957 and leaves remainder = 1
(1957 - 1) = 1956 is completely divisible by that greatest number
Factorization:
936 = 2³ × 3² × 13
1956 = 2² × 3 × 163
Then the greatest number which divides 943 and 1957 and leaves remainder 7 and 1 = HCF of 936 and 1956 = 2² × 3 = 12