if a red blood cell is 5.76 millimeters in diameter when magnified 800
times under a microscope than what is the diameter when magnified 1 time?
If it's only magnified 1 time, then it isn't magified at all.
So, you need to take the size when magnified and reduce it by a factor of 1/800.
5.76mm x (1/800) = your answer
If you need further help, please post back.