[填空题]
A box weighing 77.0 N restqo(y8atnb- hc 4kcw .2s on a table. A rope ti m3:9jfyxa;x led to the box runs vertically upward over a pulley and a weight is hung from the other end (Fig. 4-40). Determine the force that the table exerts on the box if the weight hanging on the ot;a:9 ymx3xfljher side of the pulley weighs
(a) 30.0 N ,
(b) 60.0 N ,
(c) 90.0 N .
