Eighty percent of a roof, or 2800 square feet of the roof, has been re-shingled. What is the total area of the roof?
A 35,000 sq ft
B 22.400 sq ft
C 3500 sq ft
D 2240 sq ft

a) 35,000 sq ft

Step-by-step explanation:

x = total area

the question is: 80% of what number equals 2800

.8x = 2800

x = 2800/0.8

x = 3500

it's equivalent, so we can say that its equal.

let's call the denominator x and the numerador is 18 less then denominator, x - 18.

multiply

2.x = 5.(x - 18)

2x = 5x - 90

90 = 5x - 2x

90 = 3x

x = 90/3

x = 30

so: