A research study examined the blood vitamin D levels of the entire US population of landscape gardeners. The population average level of vitamin D in US landscapers was found to be 36.78 ng/mL with a standard deviation of 5.87 ng/mL. Assuming the true distribution of blood vitamin D levels follows a normal distribution, if you randomly select a landscaper in the US, what is the probability that his/her vitamin D level will be 19.56 ng/mL or less