HELP DRAWING symmetrical double arches!

Hey guys, we had a guy walk out on us here at my job. Essentially we use CorelDraw9 for making custom shapes for multi-million dollar homes. After drawing the desired shape on CorelDraw, we then send it over to another program to be cut with hot wires, and using foam as our base material. 

My questions are, and as well if anyone can send me tutorials on all the components of CorelDraw,

1] Is there a mathimatical formula, or a simplified way for finding the angles and rises of particular arches other than Radius= (Height squared + 1/4Length of chord squared) / 2 height, i need help drawing a arch's with double lines connecting, for example I need a arch to go over a window on a house, its 74" wide, has a 10" rise, and needs to be a 6" band all the way around. My issue is i cannot maintain a even 6" all the way around, on segmented circles ect. This has been a very tedious process, and i prefer if i didn't have to use math since i'm not the best at it yet this isn't a issue. 

2] Are there FREE or cheap addons for this program to make architectural designing easier? 

3] I am fairly new with this program, I am pretty computer savvy, and really need help. Thanks guys! 

Trim Tech

-Jon