When use Voltage divider in circuit analysis
I'll just give a hint here - think about the voltage across R4, and how much current will flow through it. If you need to, remove R4 and work out the voltages at points 4 and 6.

If it wasn't quite as convenient (e.g. all resistor were not the same value), you can calculate the Vth and Rth (Thevenin) for R2, R5 and R3, R6 (i.e. points 4 and 6). Then work things out from there.