MATH PUZZLE: Can you replace...

A guy goes to a girl's house for the first time, and she shows him into the living room. She excuses herself to go to the kitchen to make them a few drinks, and as he's standing there alone, he notices a cute little vase on the mantel. He picks it up, and as he's looking at it, she walks back in.
He says "What's this?"
She says, "Oh, my father's ashes are in there."
He says, "Jeez...oooh....I..."
She says, "Yeah, he's too lazy to go to the kitchen to get an ashtray."