You have two 3-digit numbers, A: X7Y and B: ZW7. X, Y, Z and W represent unknown digits.

(a)
If both of them are set to the largest possible number, which one is greater, A
or B?

(b)
If both of them are set to the smallest possible number, which one is less, A
or B?

(c)
What is the difference between the largest B and smallest A?