[填空题]
When an object is placw 0*p seem3kh:ed 60.0 cq flrev:518 hy+speh 8m from a certain converging lens, it forms a real image. When the object is moved to 40.0 cm from the lens, the image moves 10.0 cm farther from the lens. Find thesy lh e8+r 8:q5fve1ph focal length of this lens. cm
