Analysis of voltage regulator circuit
For this theoretical circuit, the output voltage will be around: 
$$V_O = 6V \cdot (1 + \frac{12\textrm{k}\Omega}{24\textrm{k}\Omega}) = 9V$$ 

Hence the output current is: \$I_O = \frac{9V}{10\Omega} = 0.9A\$

The power dissipation is \$P \approx (V_{IN} - V_O) \cdot I_O = 5.4W\$ 

I assumed that \$I_C \approx I_E\$ because \$\frac{I_C}{I_E} =  \frac{I_C}{I_B+I_C} = \frac{ \beta I_B}{I_B +\beta I_B} = \frac{ \beta I_B}{(\beta +1) I_B} =\frac{ \beta}{\beta +1} \$ 

So if the beta is large we can assume that \$I_C \approx I_E\$  

And now you should be able to calculate the power dissipated in the transistor after voltage increases.