max gain 是$2.5，为什么解析说可以得到$5 profit?

NO.PZ2020021203000094 问题如下 A trar creates a bespreusing put options with strike prices of US25 anUS30 anthe same time to maturity. The options cost US2 anUS4.50 (respectively). Unr whcircumstances will the tra profitable? It costs US2.50 to set up the besprea If the asset priis between US27 .50 anUS30, the payoff from the sprewill less thUS2.50. If it is less thUS27.50, the payoff will between US2.50 anUS5. Thus, the tra will profitable if the priof the asset maturity is less thUS27.50. 想请问一下老师，为什么这道题就自然地讨论股票价格小于27.5和大于27.5的情况，答案看明白了，但是不知道怎么想到27.5

NO.PZ2020021203000094 问题如下 A trar creates a bespreusing put options with strike prices of US25 anUS30 anthe same time to maturity. The options cost US2 anUS4.50 (respectively). Unr whcircumstances will the tra profitable? It costs US2.50 to set up the besprea If the asset priis between US27 .50 anUS30, the payoff from the sprewill less thUS2.50. If it is less thUS27.50, the payoff will between US2.50 anUS5. Thus, the tra will profitable if the priof the asset maturity is less thUS27.50.