Question

Dawn and Myrna’s father has asked them to build a rectangular pen for their dog. They have 74 feet of fencing. They want the length to be one more than twice the width. Use the 5-D Process to help Dawn and Myrna find the dimensions (both length and width) of the pen.

Answer 1

I have no idea what the "5-D Process" is.  However:

2W = L-1
2W + 2L = 74

Add 1 to both sides of the first equation to isolate L.
2W+1 = L

Now substitute this value for L in the second equation:
2W + 2(2W + 1) = 74
2W + 4W + 2 = 74
6W + 2 = 74
6W = 72
W = 72/6 = 12

L = 2W + 1 [from above] = 2(12) + 1 = 24 + 1 = 25.

25 is one more than twice the width.  25 + 25 + 12 + 12 = 50 + 24 = 74

Answer 2

rectangle perimiter=l+l+w+w=2l+2w
perimiter=74
they want legnth to be  1 more than twice width
l=1+2w
subsitute
74=2(1+2w)+2w
distribute
74=2+4w+2w
add like terms
74=2+6w
subtract 2 from both sides
72=6w
divide both sides by 6
12=w
subsitute
l=1+2w
l=1+2(12)
l=1+24
l=25

legnth=25 ft
width=12 ft
I dunno what the 5-D process is