Download the Zakat and Ushur Ordinance from the link:http://www.cdcpakistan.com/fck_image..._ordinance.pdf
20-30% will be covered if you understand the concepts in it.
Secondly, read G.K related to Islamiyat.
And finally the General Knowledge from the book you have for G.K, The best one is Carvan's G.K Book. This is the easiest way.
If you don't do so, simply buy a specific book for the above post by Bhatti Publishers. It will cater your needs.

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"But screw your courage to the sticking place,
And we'll not fail." _Shakespeare, 'Macbeth')