network theorem

In the circuit given below, the value of R requiredfor the transfer of maximum power to the load having a resistance of 3 ohm is [/img]http://i36.photobucket.com/albums/e18/rjanand38/kite_zps5e36f5a8.jpg[/img]
a) 0
b) 3 ohm
c) 6 ohm
d) infinity

my doubt here is i got two answers
1) 0, as according to power transfer theorem load should be variable but here source resister itself is variable.
2) 6 ; source resistance = load resistance
clarify...................