This site is not set up to provide answers to homework assignments.
There are essay sites on the internet that will do that for you for a fee. Though the use of such paid-for answers is, in my opinion, ethically questionable
Because this site is free to use, many students have posed questions that are, in reality homework assignments. You are not the first.
Those of us who have gone through some semblance of an education process have gained some appreciation of the lengths your teachers go to in their efforts to persuade students to think for themselves.
If you are seeking some clarity on the question, then you should be thinking of practical measures to eliminate experimental bias from the set-up, as suggested in the question.
The final paragraph is seeking ideas for experimental practice that might deliver a statistically valid result, such as an estimate of the number of times the experiment should be run, together with the statistical analysis that produced your estimate of the number of runs.
Good luck :)