The forward edges in $\pi $ are $(s,v_2)$, $(v_2,v_3)$, $(v_1,v_4)$, and $(v_4,t)$. The backward edge is $(v_1,v_3)$. We can form augmenting paths different from $\pi $ by replacing $(s,v_2,v_3)$ with $(s,v_3)$, by replacing $(v_3,v_1,v_4)$ with $(v_3,v_4)$, or by replacing $(v_3,v_1,v_4,t)$ with $(v_3,t)$, but these last two substitutions conflict with each other. Thus, there are $2\cdot 3 = 6$ possible augmenting paths. The maximum flow starts with the flow of the (b)-figure and adds one unit of flow along $(s,v_3,t)$ and one additional unit of flow along $(s,v_2,v_3,v_4,t)$. At this point, there are no augmenting paths left. Therefore, the maximum flow has value $14$.