Voltage Divider

$V_x=\frac{R_x}{R_T}\ast V_T$

$V_x=$ the Voltage across the designated resistor

$R_T=$ the resistance for into the specific part of the circuit (so in parallel, it would be the voltage INTO the parallel portion)

$4.5v=\frac{1k\mathrm{\Omega }}{1k\mathrm{\Omega }+x}\ast V_{in}$