74A52B1 and 326AB4C are multiples of 3.....That means if we divide them by 3, we should get a whole number.
Lets assume A=1 and B=1,
So,
74A52B1 becomes 7415211
Now, lets divide it by 3.
7415211 / 3 = 2471737
Since we got a whole number as a quotient, we can safely say that A=1 and B=1.
∴ The second number 326AB4C becomes 326114C.
Now, lets assume C = 1.
So,
326114C becomes 3261141.
Now,
lets divide it by 3.
3261141 / 3 = 1087047
Since we got a whole number as a quotient, C = 1
∴The value of C is 1. So, answer choice A is correct.
