I totally agree with Holice. It's apparent the mother's friend has never backed a quilt. A king quilt usually requires about 9 yards of fabric. If you use John Flynn's' methods you could get away with using less.You're 3 1/4 estimate sounds about right. If these are first time quilters, the cutting/piecing needs to be kept at a minimum. If cost is an issue, maybe suggesting muslin would be more cost effective.