 So we can see that the ball starts off at the origin of Bob's coordinate system and it leaves his hand right when he starts his stopwatch, so that's at Bob's time, t equals zero. So the coordinates of the ball leaving his hand are zero zero zero in Bob's frame. So after two seconds, the ball has traveled forward six meters. It's not moved along the y-axis, so it's still at y equals zero and two seconds have elapsed. So the coordinates of where the ball is after two seconds is six meters, zero, and two seconds after Bob started time. And when the ball hits the wall, its x-position is 13.5 meters. Again, it's still along the y equals zero axis and it will hit the wall 13.5 divided by 3, which is 4.5 seconds after Bob started time. So what about in Alice's frame? So the ball leaving Bob's hand happens 20 meters behind Alice's origin. So the x-coordinate of that is minus 20. The y-coordinate is zero and this happens two seconds before Alice starts timing. So in Alice's t-axis, the time coordinate is minus two seconds. So after two seconds, the ball has traveled forward six meters, so it's minus 14 meters, 14 meters behind Alice and the time has advanced two seconds, bringing it to what Alice calls t equals zero. And lastly, when it hits the wall, that event occurs six and a half meters behind Alice, so minus 6.5 and 2.5 seconds after the time Alice calls t equals zero.