Susan Williams has been the production manager of Medical Supplies, Inc

Susan Williams has been the production manager of Medical Supplies, Inc. for the past 17 years. Medical Supplies Inc. is a producer of bandages and arm slings. During the past 5 y ears, the demand for No-Stick bandages has been fairly constant. On the average, sales have been about 87,000 packages of No-Stick. Susan has reason to believe that the distribution of No-Stick follows a normal curve, with a standard deviation of 4,500 packages. 
a. What is the probability that sales will be less than 80,000 packages?