A lens of focal length 40 mm is mounted on a 35 mm camera.

A lens of focal length 40 mm is mounted on a 35 mm camera. the lens aperture is set at f/5.6 and the shutter speed set at 1/250 s. a different camera has a lens of focal length 56 mm in place. the shutter speed is set at 1/60 s. the lens aperture setting, for the closest matching film exposure, is: