In a restaurant, one cook slides a 215-g delicious pizza down the counter from left to right at 1.63 m/s. At nearly the exact same time, another cook launches a 349-g cheeseburger along the same counter from right to left at 2.10 m/s. The two items collide head‑on at the given speeds – the counter is friction‑free due to accumulated grease – and combine into a single, wonderful concoction. At what speed does the dish move?