Calculate the Voltage Drop

British Standard 7671 gives full details.

You should start by taking lessons on how to search the internet using Google.

http://www.google.com/webhp?sourceid=toolbar-instant&hl=en&ion=1&qscrl=1&nord=1&rlz=1T4ADFA_enUS493US493#hl=en&gs_nf=1&gs_mss=hvoltage%20drop%20in%20the%20transmission%20line&cp=37&gs_id=m&xhr=t&q=voltage+drop+in+transmission+line&pf=p&qscrl=1&nord=1&rlz=1T4ADFA_enUS493US493&sclient=psy-ab&oq=voltage+drop+in+the+transmission+line&gs_l=&pbx=1&bav=on.2,or.r_gc.r_pw.r_qf.&fp=7543522d97c65030&ion=1&biw=1427&bih=541&bs=1

This really sounds like University-level power engineering homework, did you not pay attention in class or read your course literature?

Have you tried a simple internet search for your answer, there are plenty of resources on the web other than asking people who actually work in the power transmission industry to tell you how?

_{Jack - One of those people who work in the power transmission industry.}