//example 7 pagenumber 142
clear
q=4.5*10^22;//atoms per cubic metre
na=q/(10^4);
eo=0.026*24.16;
e=1.6*10^-19;
W=sqrt((4*16*0.628)/(36*3.14*10^9*na*10^6*e));
disp('width   =   '+string(W)+'metre');