Electrons move in the direction opposite to current.

$$ V - V_1 - V_2 - V_3 = 0 \Rightarrow IR = IR_1+IR_2+IR_3 $$

$$ R_s = R_1+R_2+R_3 $$

$$ I = I_1 + I_2 \Rightarrow \frac{V}{R_p} = \frac{V}{R_1} + \frac{V}{R_2} $$

$$ \frac{1}{R_p} = \frac{1}{R_1} + \frac{1}{R_2} $$

$$ \varepsilon - IR - \frac{q}{C} = 0 \Rightarrow \varepsilon - R\frac{dq}{dt} - \frac{q}{C} = 0 $$

$$ \frac{dq}{dt} = \frac{C\varepsilon-q}{RC} \Rightarrow \int $$