Remember that mulches such as wood chips control annual weeds like purslane and knotweed very well. Mulching to control a vigorous creeping perennial like Canada thistle or bindweed is NOT effective. See CSU Extension fact sheet #7.214 on Mulches.
3.5 feet X 25 feet is 88 square feet. 9 cubic yards of mulch will cover 1000 sq ft with a 3 inch depth of mulch, the recommended mulch depth. Doing the math conversion, you'll need 0.8 cu yds of mulch to cover your 88 sq ft area with a 3 inch mulch depth. After it is applied, sprinkle mulch to help it settle and become less prone to wind blowing. As lower layers of mulch (in contact with soil) decompose and upper layers become sun-bleached, you may want to add some mulch every other year to "renew" it.
