A box of oatmeal must contain 13 oz. The machine that fills the oatmeal boxes is set so that, on average, a box contains 13.8 oz. The boxes filled by the machine have weights that can be closely approximated by a normal curve. What proportion of the boxes filled by the machine are underweight if the standard deviation is 0.4 oz? Click here to view page 1 of the table of areas under the standard normal curve. Click here to view page 2 of the table of areas under the standard normal curve. The proportion is. (Type an integer or decimal rounded to four decimal places as needed.)