By KVL the sum of voltages across R1,R5 and R6 should equal 36.
you know voltage across R6 and R1 (IR1 X R1) .subtract this from 36 and you will get the voltage across R5,divide this by R5 to get the current through R5.
Subtract this from I total (30 ma) to get current through R2 (in series with
R3||R4).Since this combination is parallel with R5 their voltages are equal.
Divide this voltage by the calculated current to get the total resistance .
subtract the value of R3||R4 you already got from the total value to get R2