Hi Joao, the decision is whether to exercise BEFORE the dividend is paid (in which case you get 25-21.25=3.75) or keep the option alive (in which case you have an option with 7.53). In these setups we always need to make an assumption about when you can exercise (just before or after the dividend is paid). The former matches better with our replication strategy, because if you buy some stock to replicate at time 0, you will get some dividends. (And if you sell short some stock to replicate, you need to pay the dividend.)
M