How do I find the starting water temperature?

Well, either measure it with a thermometer before the experiment, or subtract from the final temperature how much the water has heated.
The temperature can also be found based on the formula Q = cm (t1-t2)
where t1 is the initial temperature and t2 is the final temperature, then
t1 = (Q / cm) + t2



One of the components of a person's success in our time is receiving modern high-quality education, mastering the knowledge, skills and abilities necessary for life in society. A person today needs to study almost all his life, mastering everything new and new, acquiring the necessary professional qualities.