# Can't Understand the formula for processing speed of each job

I am trying to understand the formula for processing speed of each job. I got the formula from the following link:

The other details are provided below:

I can't understand what is the basis (i.e. the fundamental logic) of the following formula. Speed (i.e. Velocity) is given by : S= V * t

Why we have this fraction term in the formula? What does the denominator represent? I think it is representing the processing time of each job.