Here are my calculations, assuming that you can buy enough yardage so you do not have to piece the borders. (In other words, you would be cutting each strip along the selvedge edge rather than our more common cutting of width-wise strips.) This is assuming that by "stripe" you actually mean border. If by "stripe" you mean "striped fabric" then I am assuming that you want the fabric strips running parallel to the quilt edges.
I am also assuming that your 76 inches by 62 inches are exact measurements of your quilt top (which means that these measurements include enough for a seam allowance).
First 6-inch brown border requires:
2 strips that are 6.5" wide and 76" long
2 strips that are 6.5" wide and (62 + 6.25 + 6.25)" long = 74.5" long
Second 4-inch white stripe border requires:
2 strips that are 4.5" wide and (76 + 6.25 + 6.25)" long = 88.5"
2 strips that are 4.5" wide and (62+6.25+6.25+4.25+4.25)" long = 83"
Third 6-inch brown stripe border requires:
2 strips that are 6.5" wide and (76+6.25+6.25+4.25+4.25)" long = 87"
2 strips that are 6.5" wide and (62+6.25+6.25+4.25+4.25+6.25+6.25)" long = 95.5"
95.5" equals about 2-3/4 yards of fabric. Unfortunately, you need 8 strips that are 6.5" wide which equals 52" and quilting fabric is at most 42". To not have to piece the brown borders, you would need to purchase 5.5 yards of fabric and you would have quite a bit left over.
The white fabric would require 88.5" in length, which would be about 2.5 yards if you don't piece.
It's an interesting challenge now to work out how to minimize the yardage requirements. I may have some time to do that later. (And *hopefully* my calculations above are correct. Perhaps someone else can check them and correct any mistakes. It's a little hard to scroll around in this small reply box to make sure I have not made a really stupid error.)