In the circuit shown in figure, the electromotive force of the battery is 9 V and its internal resistance is $15\Omega$. The two identical voltmeters can be considered ideal. Let $V_1$ and ${V_1}^1$ be reading of  $1^{st}$ voltmeter when switch is open and closed respectively. Similarly $V_2$ and ${V_2}^1$ be the reading of  $2^{nd}$ voltmeter when switch is open and closed respectively. Then find the value of  $\frac{{V_2}^1+V_2}{{V_1}^1+V_1}$.