The prime factors of 66 are 2.3.11, so 4a5b72 must be divisible by these factors.

Clearly it is divisible by 2.

For it to be divisible by 3 we must have a+b as a multiple of 3.

Try the simplest: a = 0, b = 3: 405372/66 = 6142.

Assuming the **sum** of a and b is unique, then a+b = 3