20
There are 10 feet of posts on each side. That means there are 40 feet of fencing in total. If you divide that by two (to represent posts being 2 feet apart) then you get 20. There are 20 posts needed.
Step-by-step explanation:
m1.m2= -1
(4y = -2x -9)= (y = -1x/2 -9/4)
-1/2.m2= -1
m2 = 2
formula = y - y1 = m2 ( x - x1)
y - 10 = 2 ( x - (-7))
y - 10 = 2x + 14
y = 2x + 24
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