Hopefully when calculating the overall resistance, you simplified the circuit to 4R/3 and R1 in parallel with 2R in series with V. This means that the voltage will be the same across R1 and 4/3R.
The parallel combination can be simplified further to 4R/7, so the voltage across the 4R/7 is the same as the voltage across R1. The voltage fraction is equivalent to V *(4/7) / (4/7 + 2R) = 2V/9.