myayden03,
consider this: yards are a measure of volume, so you are buying cubic yards, that is, 36 inches x 36 inches x 36 inches = 1 cu yard. This calculates to 46,656 cu inches to a single yard.
Convert your 360 square feet to inches. 360 square feet represent a rectangle that is 36 ft by 10 ft, which can be transposed into inches or [(36x12) x (10x12)], which
equals 432 lineal inches x 120 lineal inches or 51,840 square inches.
Now add your 3 inches of mulch. That is, 3 x 51,840 = 155,520 cu inches.
Divide that by the cu inches in one yard: 155,520/46,656 = 3.333 yards of mulch.
Usually, you have to buy whole yards, so you decide whether to buy 3 or 4 yards.
I would buy 4 and put the rest on my flower beds!
trbjr