Noelle, Sacre Cœur is close to two metro stations : Anvers on line 2 and Abbesses on line 12. Locate these metro stations and Sacre Coeur on
map of Montmartre. It will take you close to 60 minutes to get to Eiffel Tower by metro. Walk down to Anvers station. Take line 2 up to Charles de Gaulle station, then line 6 to Bir Hakeim station. Walk to Eiffel Tower. You can alternatively take a taxi, which may be faster except at rush hour. Line 12 will easily bring you to other places in Paris, including Saint Lazare train station, Concorde Square and Montparnasse train station. See Paris
metro map. Enjoy your stay in Paris.