Anyone know the answer to number 16. plz

Recognize that the volume can be found as follows:

(average height of trapezoid) * (8 ft)(13 ft) = 286 ft^3 total volume.

Then (8 ft)(13 ft) (ave ht of trap) = 286 ft^3.
                                                             286 ft^3
Solving for (ave ht of trap):  (ave ht) = = 2.75 ft
                                                               104 ft^2

Thus, [ 2 ft + (?) ] / 2 = 2.75 ft.  

Remove the fraction by mult. both sides by 2:  2 ft + (?) = 5.5 ft

Subtr. 2 from both sides, we get (?) = 3.5 ft

The missing dimension is 3.5 ft.

Best answer that i found on yahoo ok   set :   x= length of 2nd piece in cm  x- 3= length of 1st piece in cm  x-4= length of 3rd piece in cm  then since you know they all came from the 20 cm ribbon you add them together and set them equal to 20x+ x-3 +x-4 = 20  3x - 7= 20  3x= 27  x= 9  the shortest piece is the third piece which is x- 4  x-4  9-4 = 5  the length of the smallest piece is 5 cm.  the other lengths are  9 cm  6 cm