Four circles are placed as shown in the figure. At each point where two circles are in contact, they are tangent to each other. Write a program that asks for the radii of the four circles, then use them to determine the distance between the centers $C_2$ and $C_4.$ Print that distance out $($with $4$ decimal portions$).$

Use the following set of radii for the testing case: $R_1=16mm,R_2=6\mathrm{.}5mm,R_3=12mm,$ and $R_4=9\mathrm{.}5mm.$

Hint: use the law of cosines.

Use c language