You will need to specify what kind of voltage is involved. The following assumes a 10 vrms sinusoidal voltage. You will also need to know the frequency, since the impedance of a capacitor depends on frequency.
The resistance (R) of a resistor is a special case of electrical impedance (Z). The current through and voltage across a resistor are said to be “in phase”. The impedance of a resistor is simply its magnitude in ohms. That is
$$Z_{R}=R$$
Capacitors and inductors are circuit elements in which the current and voltage are 90 degrees out of phase. The magnitude of the impedance of a capacitor is called its capacitive reactance, $X_C$ and given by
$$X_{C}=\frac{1}{2πfC}$$
Where $f$ is the frequency of the voltage and C the capacitance.
Its impedance is given by
$$Z_{C}=-jX_{C}=\frac{-j}{2πfC}$$
$j$ is the imaginary number equal to the square root of minus 1. The j accounts for the fact that the impedance is -90 degrees in the complex plane. The impedance of a resistor is a real number in the complex plane.
When applying KVL to your series RC circuit, in phasor notation, you will have
$$+10-i3-iR_{1}-(-jX_{C})i=0$$
Where $i$ is the sinusoidal current, and it is assumed your 10 volt power supply is a 10 vrms sinusoidal voltage source with no phase angle (v=0 when t=0). To find the current, divide the voltage by the equivalent series impedance, $Z_{equiv}$
$$Z_{equiv} = (R_{1} + 3)-jX_{C})$$
The rest is complex number algebra.
Hope this helps.