Operations Management help needed. please check your work, provide explanation if possible. if it's right I'll give you a like.

1800 Degrees Below is a new nitrogen ice cream store with a new concept of how temperature is actually measured. The company want to be certain that their product is served at the right temperature and that it does not vary. To that end, they have their regional managers sample one store from their district each day and assess the temperature of the an outgoing item at random. The data is presented below. What is the appropriate value of the upper control limits if we do NOT know the standard deviation of the process (choose the nearest values)? 19.63 19.47 20.03 19.84 None of the above are within +10.05