b
$w _{\text {lot }}=150 \ J $
$w _{\text {lat }}=200 \ J $
$Q _{\text {lat }}=500 \ J So U _{\text {lat }}=300 \ J$
So : $U_t=400 \ J$
$U_b=100 \ J $
$Q_b=100+50=150 \ J $
$Q_{b t}=300+150=450 \ J$
So the required ratio $\frac{Q_{b f}}{Q_{i b}}=\frac{450-150}{150}=2$
