Derive the labour demand function.

Assuming a unit price $p=1$ the profit function becomes $$G=4K^\alpha L^{1-\alpha}-cK-wL$$ where w is the wage. Maximize the profit with respect to $L$ $$\frac{\partial G}{\partial L}=4K^\alpha (1-\alpha)L^{-\alpha}-w=0$$ and solve for $L$ $$L=\big(4 (1-\alpha) K^\alpha /w \big)^{1/\alpha}$$