The operation is defined for all integers a and b by the equation ab = (a - 1)(b - 1). If y10 = 90, what is the value of y ?	Choose the correct choice from the following options
A) 10
B) 12
C) 15
D) 11
E) 20

Rationale: "ab = ( a - 1 ) ( b - 1 ) y 10 = ( y - 1 ) ( 10 - 1 ) = 90 - - > y - 1 = 10 - - > y = 11 answer : d"
Answer: D