Explanation

(b) Using the relation
$\ \ \ \ \ \ \ \ \ \frac{W}{Q_{1}} = \frac{Q_{1} - Q_{2}\ }{Q_{1}}$
$\ or\ \ \ \frac{W}{Q_{1}} = 1 - \frac{Q_{2}}{Q_{1}}$
$or\ \ \ \ \frac{W}{Q_{1}} = 1 - \frac{T_{2}}{T_{1}}\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \left( \because\frac{Q_{1}}{Q_{2}} = \frac{T_{1}}{T_{2}} \right)$
$or\ \ \ \ \ \ W = Q_{1}\left( 1 - \frac{T_{2}}{T_{1}} \right)$
$\therefore\ \ \ W = 6 \times 10^{4}\left( 1 - \frac{(127 + 273)}{(227 + 273)} \right)$
$\ \ or\ \ \ \ \ \ \ W = 6 \times 10^{4}\left( 1 - \frac{400}{500} \right)$
$\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ = 6 \times 10^{4} \times \frac{100}{500}$
$\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ = 1.2 \times 10^{4}\ J$