Ghent (Belgium) (AFP) - Andy Murray ticked off one of the three boxes he needs to fill to win Britain's first Davis Cup since 1936 and now he needs the help of older brother Jamie.The two Scots will once again join forces in Ghent on Saturday in the doubles -- more often than not the key rubber in Davis Cup ties.Of the last 15 Davis Cup finals, 11 have gone to the team that won the doubles and in the Murray brothers, the British have a trump card they think they can play against Belgium. "I believe in myself.