Answer:
    k = 1.30
Explanation:
For this exercise let's write the capacitance in air and with dielectric
air       C₀ = Q / DV
dielectric  C = k Q / DV
They tell us that the capacitor is charged and then the battery is disconnected, therefore the charge stored on the plate remains constant.
            Â
therefore the capacitance a changes to the value
      C = k C₀
The voltage in the presence of dielectric must meet the relationship
      ΔV = ΔV₀ / k
      k = ΔV₀ /ΔV
let's calculate
      k = 60/46
      k = 1.30