A cylinder has volume V=pir^2h use r=8/2=4 v=16*12pi This is true because the circle has Area pi*r^2 and it is being potruded thru a distance h to make a cylinder if you can visualize that.
Read https://www.wyzant.com/resources/answers/2997/how_do_you_figure_out_how_to_determine_the_best_method... and I think that will answer your question (:
