1- the current of 500ohm is (2.5 /500 ) = 0.005 A . Since , 50 is series with 500= 550 ohm Hence voltage = (0.005 *550)= 2.75V. Since R is parallel with 550ohm , that’s mean the voltage of R is 2.75V, and voltage of (550R/550+R) is 2.75V. Since total voltage is 12 V that’s lead voltage of the first 550 ohm is (12-2.75)= 9.25V =====> I = (9.25/550)= 0.0168A. Since (R is parallel with the second 550) = 550R/550+R . And this (550R/550+R) is series with the first 550ohm witch means the same current passing through each one of them , so [2.75/(550R/550+R)]= 0.0168====> 550+R= 3.36R ====>R =550/2.36 = 233ohm