Answer: The correct option is
(D) 6 less than a number b.
Step-by-step explanation: We are given to write a word phrase that can be represented by the following expression :
"b - 6".
Since we are subtracting 6 from a number b, so the resulting number will be 6 less than b.
Thus, the required word phrase foe the given expression is
"6 less than a number b".
Option (D) is CORRECT.