 So YA is just YB, and our expression for delta TA is substituting it in. And then as before, we just divide by delta TB. And there we had it. So on the numerator, we have UYB, the speed in Bob's reference frame. And on the denominator, we have two factors. One is a gamma. So this is to take into account time dilation. If Alice is moving very quickly, the rock will appear to be moving in slow motion, moving more slowly. So that's what that gamma times one represents. And we also have a minus gamma, UXBV on C squared, which is similar to our relativity of simultaneity term. On instead of a distance, we have the velocity along the X direction of the rock. So in the situation drawn, it has no motion along the X axis. It's just moving along the Y axis, in which case this reduces to UYB on gamma. Now let's say the rock is moving diagonally, meaning it has both a Y component to its motion and an X component. So in this case, the rock's position along the X axis is changing. And because of what we've said about how separations in space correspond to separations in time, this movement along the horizontal axis will change its apparent velocity.