I have to find the empirical formula

1) these are barrel shaped microtubules in most animal cells, that organize the spindles during cell division

What is the number of moles of chemical units represented by 9.03x10^24? and how do i show work? (dumb it down )

Pastoral farming is best described as a. a method of raising livestock and moving herds b. an african method of agriculture c. a method of cultivating crops on poor soils d. a common method of desert farming select the best answer from the choices provided a b c d