def velocity_transformation(frame_velocity: float, observed_velocity: float) -> float:
    """
    Computes the velocity transformation for a given frame velocity and observed velocity.
    The frame velocity is the velocity of the new frame relative to this frame.
    The observed velocity is a velocity measured in this frame.
    The returned velocity is the velocity of the observed velocity in the new frame.
    Expects velocity as a multiple of c, i.e. velocity_in_mps = c * velocity.
    """
    return (observed_velocity - frame_velocity) / (
        1 - frame_velocity * observed_velocity
    )