//Variable declaration
d=0.2*10**-3;     //seperation(m)
lamda=550*10**-9;    //wavelength(m)
D=1;     //diameter(m)

//Calculation
beta=lamda*D/d;     //fringe width(m)

//Result
printf('fringe width is %0.3f   mm  \n',beta*10**3)