Heat required : 4.8 kJ
<h3>Further explanation </h3>The heat to change the phase can be formulated :
Q = mLf (melting/freezing)
Q = mLv (vaporization/condensation)
Lf=latent heat of fusion
Lv=latent heat of vaporization
The heat needed to raise the temperature
Q = m . c . Δt
1. heat to raise temperature from -20 °C to 0 °C
2. phase change(ice to water)
3. heat to raise temperature from 0 °C to 25 °C