this is what i think:

a)The Messenger(sallallahu alaiyhi wassallam) of Allah broke camp and returned to Madinah. On his journey back, Allah confirmed that the truce of Hudaybiyyah was not a set-back but a victory:

Surely We have given you a clear victory, that Allah may forgive you your former and later sins, and complete His blessing on you and guide you on a straight path and that Allah may help you with a mighty help. (48: 1-3)

Umar (may Allah be pleased with him) said, 'Is this a victory then, Messenger(sallallahu alaiyhi wassallam) of Allah!'

He replied, 'Yes'.

The Hudaybiyyah treaty also gave the idol-worshippers and Muslims an opportunity to mix. The idol-worshippers soon came to appreciate the good qualities of the Muslims. Before a year had passed, many of them had become Muslims, and the Quraysh leaders were worried about their influence.

b)Sa`id bin Al-Musayyib was asked by Qatadah, "How many were present for the pledge of Ar-Ridwan'' Sa`id said, "One thousand and five hundred.'' Qatadah posed, "Jabir bin `Abdullah, may Allah be pleased with them both, said that they were one thousand and four hundred.'' Sa`id said, "He forgot. He told me that they were one thousand and five hundred.'' However, Al-Bayhaqi commented, "This narration testifies that Jabir used to state that they were one thousand and five hundred, but later on remembered the true number and said that they were one thousand and four hundred.''

c) i'll be back for this one, as am scared to give the right answer. i'll double check it inshaAllah