I might be confused about your post, but if your at the white stake then you have 150 yrds to the hole. You do not subtract the 150 yrd from the origunal, the 210 would have been your drive. Also there should be red stakes that will let you know that you have 100 yds left and there are even blue ones for the 200 yd. If you ball is past the marker just walk it off, your stride will be approx 1 yard and will give you an approx range. EX. Ball lands past the Red Stake, you walk off 15 paces to your ball. You have 85 yd to the center of the green. Now if the flag is at the front or back, just add or subtract an approx amount say 5 yds. This is not going to be dead on, but I doubt that many can hit any of their clubs an exact distance anyway.
Denny