How do I calculate power of this combination?
Current and voltage are linear, but power is quadratic. So you can't apply superposition on power directly. But you can find either voltage or current using superposition and then work power:  

Let \$V_1\$ be the voltage across \$R\$ when current source is open.
Let \$V_2\$ be the voltage across \$R\$ when voltage source is shorted.
Then by superposition, overall voltage across \$R\$ will be \$V_{tot} = V_1+V_2\$.  

\$P_1 = V_1^2/R \Rightarrow V_1 =\sqrt{P_1 R} \$  

\$P_2 = V_2^2/R \Rightarrow V_2 =\sqrt{P_2 R} \$  

\$P_{tot} = V_{tot}^2/R=(V_1+V_2)^2/R = \dfrac{(\sqrt{P_1R}+\sqrt{P_2R})^2}{R}=(\sqrt{P_1}+\sqrt{P_2})^2\$