Each width of fabric should be at least 42". So, you'll be able to make 4 blocks from each WOF strip set. (42/9.5")
At 4 blocks/WOF strip set, to make a 9x10 block quilt, you'll need 90 blocks, or 23 strip sets (90/4, rounding up)
And each strip is 3.5", so you need 3.5" x 23 = 80.5" Divide by 36" to get yardage = 2.24 yards.
I'd buy 2.5 yards in case of cutting errors (yours or the shop's).
If you want the quilt a little bigger, that's 10x11 blocks, or 110 blocks. Comes to 2.72 yards. I'd buy 3 yards.
Those are the yardages for just the blocks, for each of the 3 colors.
If you're using the same fabric for borders, you'll need more. I would try to cut the fabric for the borders lengthwise. 3 yards more would be enough for a 100" length quilt. 3.25 yards if you want one more block. This will leave a lot of unused fabric for the borders. You can get by with less if you want to piece the borders. This will use 3.5" x 4, or 14" of the fabric width for the wide border. That's one third of the 42" width. So, three pieces per border will use one third the fabric plus a little for butt seaming, more for diagonal seaming.