A `1kg` block `B` rests as shown on a bracket `A` of same mass. Constant forces `F_(1)=20N` and `F_(2)=8N` start to act at time `t=0` when the distance of block `B` from pulley is `50cm`. Time when block `B` reaches the pulley is `……………………` .`(` Assume that friction is absent every where. Pulley and string are light.