Find the value of r2 in the voltage divider, which would give an output voltage of 2.0v
Vin=6.0v
R1=3.0 (resistor)
R2=?
Vout=2.0v
the two resistors are in a line and the out voltage is take from r2
Substitute into the voltage divider formula you will undoubtedly have in your class notes or textbook. If you need more help, please show your work and say where you get stuck.