The probability in question is the area under the standard normal probability distribution between 98.4 degree F and infinity, and intuitively you can detect that this will be more than 0.5 (corresponding to 50%).
Convert 98.4 degrees F to a z-score, using the sample standard deviation (0.10 degree F). That z score is
z = ————– = -0.20/0.10 = -2
We need to determine the area under the standard normal curve to the right of z=-2. Use a table of z-scores to do this, or use your calculator’s built-in probability functions. My result is 98.21% (corresponding to an area of 0.9821).
With my calculator I can find this probability using the following command: