kill(all)$

fpprintprec:4$

m(x1,y1,x2,y2):= (y2-y1)/(x2-x1);

b(m, x1, y1):=y1-m*x1;

y:m(815,63,860,64)*832.230 + b(m(815,63,860,64),815,63);

float(%);

(y-63)*365.25;

day:round(%);