How many yards of dirt will I need to cover an area 47 feet wide by 6 feet ,1 foot deep at the back slopping to zero at the front?

The area of a right angle triangle is 1/2(L x W).  The volume of a right angle wedge is 1/2 (L x W x H)  Your Length is 47ft, your Width is 6 ft, and your Height is 1ft.

1/2 (47 x 6 x 1)
= 1/2 (282)
= 141 Cubic ft.

A yard of dirt is 3ft x 3ft x 3ft or 27 cubic ft.

So 141/27 = 5.2 Yards

5.2 yards of dirt will spread an area 47ft long, 6ft wide, and sloping from 1ft deep down to 0.

Good luck with the project.