Pulley 1 rotates about axis A of link 2 which carries load 3. Flexible l ink (rope) 4, attached at point C, runs over pulley 1. In lifting load 3, point B is moved parallel to axis y-y. The displacement of point B is s_B=2s_A , where s_A is the displacement of point A. Consequently, the block and tackle has a mechanical advantage of 2.
$3518$SFL,MH$