Which two of the following lenses could be used to construct a telescope? Focal lengths: 20cm/1cm/100cm/5cm/10cm/2cm/25cm/75cm (a.) That magnifies 20x and has a length of approx 1.0m (b.) magnifies by 15x (c.) magnifies 50 x I used magnification=telescope focal length/eye peice length (Lense) but am confused when they save two of the following lenses can be be used??