% Example 1_2:  Explore how the surface area of a sphere
% changes with an increase in the radius.

r= input('Enter radius r in miles: ');
delta= input('Enter delta r in inches: ');
newr= r + ((delta/12)/5280);  % new radius in miles
A= 4*pi*r^2;                  % original surface area
newA= 4*pi*newr^2;            % new surface area
incr= newA - A;               % increase in area
fprintf('Increase in area (mile^2) is %f.\n', incr);