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Let the number be abcd
ad = 0       ________ (i)
|a – d| = 7       ________ (ii)
bc = 18      ________ (iii)
a – d = b – c   ________ (iv)
Since a x d is 0 then at least 1 digit out of a & d must be 0 but a ≠ 0 otherwise the number will not be a 4 digit number 
So, d = 0
a – d = 7
a – 0 = 7
a = 7
bc = 18
b – c = 7
b = c + 7 
(c + 7)(c) = 18
c² + 7c – 18 = 0
c² + qc – 2c – 18 = 0
c(c + q) – 2c – 18 = 0
(c – 2)(c + q) = 0
c = 2, – q
c can’t be negative as it is a digit
c = 2
b = c + 7
b = 2 + 7 
b = 9
Number = abcd = 7920