Here's how I determine how much fabric is needed for my binding.
Take the length + width x 2. 68+93 = 161 x 2=322. Then divide that total by the width of your fabric. 322 divided. By 40 (on normal 42" fabric) = 8.05, which is how many strips of 40 inch fabric is needed for the 322 inch total length.
Now you need to determine how much fabric is needed, depending on the width of you binding. For 2 1/2 inch wide binding, take the 8.05 x 2.5 = 20.5 inches. I usually add another strip or two, just in case. So I would go for 24 inches or 2/3 of a yard.
Hope this helps for future binding needs.
Are you another math teacher? That's the same description I would have given! (And considering how much trouble my local grocery clerks have figuring a rain check, we need better math education!)