The yield, in tons of ore per day, at a given coal mine is approximately normally distributed

Question:

The yield, in tons of ore per day, at a given coal mine is approximately normally distributed with mean 785 tons and standard deviation 60. Find the probability that at least 800 tons of ore will be mined on a given day. Find the proportion of working days in which anywhere from 750 to 850 tons is mined. Find the probability that on a given day, the yield will be below 665 tons.