250 knots, is 4.2nm/min roughly so 30/4.2 is 7.2 minutes or 10000/7.2=1380 fpm. for arguments sake just do the 3/1 ratio at 1/2 the GS add a zero so 10*3 distance 250/2+125*10 1250 fpm close enough for government work. If your really a keener add 3-5 nm to slow down depending on wind