A Marketing Research Application Uses the Variable HD to Represent $\ge$

A marketing research application uses the variable HD to represent the number of homeowners interviewed during the day. The objective function minimizes the cost of interviewing this and other categories and there is a constraint that HD $\ge$ 100. The solution indicates that interviewing another homeowner during the day will increase costs by 10.00. What do you know?

A) the objective function coefficient of HD is 10.
B) the dual price for the HD constraint is 10.
C) the objective function coefficient of HD is -10.
D) the dual price for the HD constraint is -10.