The first thing in these kinds of problems is to come up with a statement (statistical that is) that differentiates between a positive result that contributes to one decision and another that contributes to its complement.
In your question you are trying to see whether the sore throat is the reason, but how do you evaluate this? You can't really make a conclusion of this even with the limited information you have.
But what you can do is provide evidence that people with sore throats have abnormal temperature in that the abnormal temperature is statistically significantly different from the normal temperature and this is given by a 1-sample t-test where you are comparing whether the population mean of a sample is statistically significantly similar or different from a particular value.
The value you are testing is the normal temperature which is 98.4F where the sample mean 98.9F with a standard error of 0.5F. Your test will be that H0: mu = 98.4 and H1: mu != 98.4.
Before we continue what do you know about 1-sample t-tests?