If the company haven't ever hired a TFW before, then they don't need to complete Schedule E, the cap is automatically 10%.
If they do, then they'll have to complete it in order to find their current cap. The calculation is basically the total hours worked by all TFWs weekly divided by the total hours by everyone in the workplace (including the TFWs) x100. The weekly hours are calculated by taking the total hours from 4 consecutive weeks and dividing it by 4 to find the average weekly. If you just follow the steps in the form, you'll get the number.
But in essence, as above, if they already have more than 10% then they can't hire any more, unless the work permit of one of them is expiring within 3 months and they'd just like to replace them.