To now the power we need to:
[tex]P=\frac{E}{t}=\frac{F\cdot d}{t}=\frac{20N\cdot10m}{25s}=8W[/tex]The power is the ratio of energy over time, and the energy is the force applyed in the distance
For the efficiency
[tex]\eta=\frac{75J}{20N\cdot10m}=0.375[/tex]