In a laundry, 0.45 kg of steam at 100 °C condenses inside the pipes of a pressing machine and…

Step 1. The idea. Steam turning back into water at the same temperature gives out its latent heat of vaporisation.

Step 2. The heat. $Q = mL = 0.45\ \text{kg} \times 2.26 \times 10^{6}\ \text{J/kg} = 1.017 \times 10^{6}\ \text{J} \approx 1.02 \times 10^{6}\ \text{J}$.

Why steam is used. So much heat comes out of a small mass of steam that it heats the plates of the machine quickly.