The operation is defined for all integers a and b by the equation ab = (a - 1)(b - 1). If x9 = 160, what is the value of x ?	Choose one:
A) 18  B) 15  C) 17  D) 19  E) 21
ab = (a - 1)(b - 1)   x9 = (x-1)(9-1) = 160 --&gt; x-1=20 --&gt; x=21   Answer: 21
<result>E</result>
The operation is defined for all integers a and b by the equation ab = (a - 1)(b - 1). If x9 = 160, what is the value of x ?