Answer:
DE = 81
Step-by-step explanation:
The sides of a rhombus are congruent , thus
9z = z + 72 ( subtract z from both sides )
8z = 72 ( divide both sides by 8 )
z = 9
Then
BC = 9z = 9 × 9 = 81
Since the sides are congruent, then DE = 81
The equation of a line that passes through

and has a slope of m is

so given the point (3,1) and slope -2
(3,1), (x1,y1)
x1=3
y1=1
m=-2
the equation is