Answer :

AL2006
6 inches = 1/2 foot

Volume of the flower bed = 4-ft x 25-ft x 0.5-ft = 50 cubic feet

1 cubic yard = 27 cubic feet

Volume of the flower bed = 50/27 = 1 and 23/27 cubic yards, about 1.85 yd³ .

Rounded to the nearest cubic yard, that's 2 of them.