IQ scores

#1
Assume that adults have normally distributed IQ scores with a mean of 100 and a standard dviation of 15. Find the probability that a randomly selected adult has an IQ between 73 and 127.

In my book it says i can use my TI-83 plus. I am using: normalcdf(15, 100) to come up with the z score but that is not working. Can someone help?