The operation is defined for all integers a and b by the equation ab = (a - 1)(b - 1). If x20 = 190, what is the value of x ? Choose the most appropriate option:
A) 10	B) 12	C) 11	D) 13	E) 14

Rationale: "ab = ( a - 1 ) ( b - 1 ) x 20 = ( x - 1 ) ( 20 - 1 ) = 190 - - > x - 1 = 10 - - > x = 11 answer : c"
Answer: C