 So let's say I'm sitting in my room. Now I have my own frame of reference where the origin is right here where I am. Now I have my axes, maybe the y-axis goes in that direction and the x-axis goes in that direction. Okay, so my phone rings. Now where's my phone? It's right here. So the coordinates of that first notification are 00, the origin. Now one second later I get a second notification still from my cell phone which is still located here at the origin. So what are the coordinates of that second notification? They are 0, 0. Right? Both of these events happened at the same place. But if there was an astronaut floating up there in space, they would disagree. Because in the second that elapsed between the two notifications, the earth would have moved 30 kilometers. So from the astronaut's point of view, there's a whole 30 kilometers between those two events happening. So when I say both events happened at the same place, they both happened at the origin, I mean relative to my frame of reference which moves with me. So here we have Alice. Alice is standing at the back of a train and in this problem we're going to be describing things using Alice's frame of reference which moves together with her. Now on the opposite side of the train is Alice's friend Carl. Carl throws a ball towards Alice and Alice sees it approaching at 10 meters per second. Now in Alice's frame of reference relative to her, what speed does she see herself as having and what speed does she see the train as having?