Brent has a pet sitting business that offers two services, short visits and extended visits. The sales mix in terms of sales dollars is 70% and 30%, respectively. The sales mix in terms of units sold is 30% and 70%, respectively. Respective unit contribution margins are $40 and $60. The weighted-average unit contribution margin is

A : $54.

B : $50.

C : $40.

D : $46.