miraiah
10

4. Area of a disk of diameter D : $A= \pi*(D/2)^2\approx3.14*(3.5)^2=38.465$ Assuming that you use the usual convention of rouding 5 to the greater number :  A=38.47 5. Diameter of a circle of radius r : $A= \pi D=47$ hence $D\approx47/3.14\approx14.97$