A Very Brady 3 Way

You find yourself as Greg Brady standing in your kitchen.
Let's see you think to yourself The family is away for the weekend except for Marcia and you. You had an interveiw at State College which you aced and Marcia had to work last night at the ice cream parlor.
You look out the screen door and see Marcia and Debbi sunbathing on a blanket. They laying on their stomachs with their tops untied. Debbi is really a groovy chick who's happening in a far-out way. She's about 5'6" with shoulder length brown hair with c cup tits and a nice ass. You went out a couple times but only got to feel her up under her shirt at the drive-in. And your step-sister, she's been giving you blue balls since you were 13.
Debbi sits up and you grabs the lotion and starts applying it Marcia's back.
I've got to get in on this. You open the door and Marcia rolls over for Debbi to start massaging her breasts.
"Took you long enough to join us Greg" says a breathless Marcia
"Yeah Greggie. I'm ready for more now..." purrs Debbi licking her lips.
Marcia or Debbi?