clear
//
//
//

//Variable declaration
lamda=6000*10**-8     //wavelength(cm)
Dm=0.65     //diameter of 8th ring(cm)
Dn=0.35     //changed diameter of 8th ring(cm)

//Calculation
R=(Dm**2-Dn**2)/(4*lamda)     //radius of curvature of lens(cm)

//Result
printf("\n radius of curvature of lens is %0.0f  cm",R)
printf("\n answer given in the book is wrong")