I would like to get some help in finding a proportion considering that :

mean = 70 inches

standard deviation = 2.8 inches

What proportion of men are less than 68 inches tall? By the way , does someone can tell me what to do in order to do this problem with a ti-84/83 using the function called normalcdf ? Because I don't want to use the standard normal table (Rofl). Thanks in advance.