Good actions of a woman who travels without a mahram being affected

Q: There is a hadith about women travelling, Abu Hurairah (radhiyallahu anhu) reported: The Messenger of Allah (sallallahu alaihi wasallam) said, 

"It is not permissible for a woman who believes in Allah and the last day to make a journey of one day and night unless she is accompanied by a mahram (husband or male relative whom she is prohibited to marry)." (Al Bukhari and Muslim) 

According to the hadith, if a woman travels alone will her prayers not be accepted?

Calculating zakaat on a rate that is more beneficial for the poor

Q: We are having an economic meltdown in our country. Due to lack of forex reserves, there is a vast difference between the dollar in the bank and the dollar on the black market. Due to scarcity, majority of the people are dealing with the black market rate which is very high in comparison to the bank rate. The bank also sometimes charges a premium that brings it close to the black market rate. The whole economy is running on the dollar and things change according to the rate. 

The issue comes about when calculating zakaat and other financials. Some Ulamaa have taken what they call a middle rate to benefit the masses. Others are taking the bank rates. Yet still some are of the opinion that the black rate should be taken into consideration because everyone is using it. What should be done in this case? What rate should we use? Your advice will be greatly appreciated.

Missing salaah due to shopping

Q: If a woman is out with her family to a hotel to eat and went to a mall to enjoy some time... So what must she  do if salah time is due? She prayed asr at home and went outand now it's maghrib time and she can't pray because there is no women's prayer room in the malls or hotels... So what must she do in this situation?

If she does jama' salah in her home, like praying 4 rakah of asr and then 3 rakah of maghrib in the same time because she won't get a place to pray maghrib, is this correct?