b) The heat absorbed by the engine is [tex]Q_{in} = 1.98 \cdot 10^5 J[/tex] while the heat expelled is [tex]Q_{out} = 1.49 \cdot 10^5 J[/tex], therefore the work done by the engine is the difference between the heat absorbed and the heat expelled:
[tex]W=Q_{in} - Q_{out} = 1.98 \cdot 10^5 J - 1.49 \cdot 10^5 J = 0.49 \cdot 10^5 J[/tex]
a) The efficiency of the engine is the ratio between the work done by the engine and the heat absorbed, therefore:
[tex]\eta= \frac{W}{Q_{in}} = \frac{0.49 \cdot 10^5 J}{1.98 \cdot 10^5 J}=0.247 = 24.7\% [/tex]
