The figure is not visible here, so the exact geometry/values are missing. However, the phrase

• “two different dielectric materials with different thicknesses $t_1$ and $t_2$”,
• “separated by a conducting foil $F$”, and
• “the voltage of the conducting foil is $V$”

indicates the standard capacitor arrangement where the conducting foil divides the system into two capacitors in series.

1. Physical model

A conducting foil placed between dielectric slabs is an equipotential surface. Hence the composite arrangement behaves like:

$C_1 = \frac{\varepsilon_1 A}{t_1}, \qquad C_2 = \frac{\varepsilon_2 A}{t_2}$

with the foil as the common junction.

If the outer plates are maintained at potentials $0$ and $V_0$, and the foil is at potential $V$, then the same series charge $Q$ must satisfy

$Q = C_1(V - 0) = C_2(V_0 - V).$

So,

$\frac{\varepsilon_1 A}{t_1}V = \frac{\varepsilon_2 A}{t_2}(V_0 - V).$

Cancelling $A$,

$\frac{\varepsilon_1}{t_1}V = \frac{\varepsilon_2}{t_2}(V_0 - V).$

Solving for $V$,

$V = \frac{\dfrac{\varepsilon_2}{t_2}}{\dfrac{\varepsilon_1}{t_1} + \dfrac{\varepsilon_2}{t_2}} \, V_0.$

Equivalently,

$V = \frac{\varepsilon_2 t_1}{\varepsilon_1 t_2 + \varepsilon_2 t_1} \, V_0.$

2. Issue with the given data

The problem statement provided here does not include:

• the figure,
• values of $\varepsilon_1, \varepsilon_2$ (or dielectric constants $K_1, K_2$),
• thicknesses $t_1, t_2$,
• or the total applied voltage.

So a unique numerical value cannot be derived from the visible information alone.

3. Comparison with stored answer

The stored correct answer is 60. Since the actual numerical data/figure are absent, I cannot independently verify that value from first principles using the provided text alone.

Thus, based strictly on the available information, the numerical answer is underdetermined.

If the missing figure contained the ratio

$\frac{\varepsilon_2 t_1}{\varepsilon_1 t_2 + \varepsilon_2 t_1} V_0 = 60,$

then the foil potential would indeed be $60\,$V.