Can somebody me with these to questions how do you find the area of the circle

13)

Circumference (C) = 2π·r

11π = 2π·r

11/2 = r

Area (A) = π·r²

             =  π·(11/2)²  

            = 121π/4

           ≈ 94.985 in²

14)

diameter = 2r

          42 = 2r

           21 = r

Area (A) = π·r²

             =  π·(21)²  

            = 441π

           ≈ 1384.74 in²

$280/1384.74 in²

x = $0.20

about 20 cents per square inch

not only in mathematics, scientific proof also are required in the other field of science. also maths proofs are of particular structure, containing steps and logics. so proving is like doing science, it is science. that's why it is important to prove. 

an inaccurate proof leads to errors, or stating results that are not accurate.  which wil mess the probelm up you dont want this