Tony had to wonder as well, with a pensive pout, because Cal probably didn't even know what a car was, at least not the kind that Billy had sitting on the beach. He still felt optimistic that the kid could figure out his way around the thing, so that furrow of Tony's brow was easily gone for him to nod with a sharp breath, then a thumb over his shoulder for the sudden big, shimmering display in the air of the formula. "One is always a good start," he was happy to encourage. "You let me know when you figure out how to stop there, I've never worked out the math on that part."