Answer:
D. 21
Step-by-step explanation:
replace 21 for r, 4(21)=84
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Answer:
perimeter of the rectangular ground floor
=2(length+width)
length=X+200
width=X
=2(X+200+X)
=4x+400
4x+400 =780
4x =780-400
4x =380
x =95
width=95 feet
length=95+200
=295 feet