t=520;

>> n=2;

>> r=5;

>> p=1000;

>> x=n*r*t/p;
a=1; , b=2;
>> y=n*r*t/(p+a*n^2/x^2))+n*b;
while abs(x-y)<= 0.001
x=y;
y=n*r*t/((p+a*n^2/x^2))+n*b;
end