The power generated (MW) by liquid hydrogen turbo pumps, given to the nearest tenth, is grouped into a table having the classes [40.0, 45.0), [45.0, 50.0), [50.0,55.0),[55.0,60.0) and [60.0,65.0), where the left-hand endpoint is included but the right-hand endpoint is not. Find

(a) the class marks

(b) the class interval