Series/Parallel DC circuit analysis training issue
Applying Thevenin's theorem is often a good approach as another answer has shown.

Another approach is to redraw the circuit such that the solution can be written by inspection:







simulate this circuit &ndash; Schematic created using CircuitLab

Now, use voltage division to find the voltage across R4 and then voltage division again to find the voltage across R1, R2, and R3:

$$V_{R4}= 10V \dfrac{R_4||(R_1 + R_2 + R_3)}{R_5 + R_4||(R_1 + R_2 + R_3)}$$

$$V_{R1} = V_{R4}\dfrac{R_1}{R_1 + R_2 + R_3} $$