How to control Ticker Text Speed by Expression Controls

[METOV5EA7]

Hello! I am making a Ticker Text template and I need to have an opportunity to change the speed of this using one of the Expression Controls (Angle Control or Slider, maybe). For motion, I tried the expression "time" on X Position or Time Remap keyframes, it works but it seems I don't know how to control it by Expression Controls.

[METOV5EA7]

So, I use following code:

rate = 2; //value in px/sec.
value - [rate*timeToFrames(time), 0];

How can I control "Rate" by Slider, for example