\frac{\text{d}}{\text{d}x}[c(ax^{n}+bx^{k})]=c\frac{\text{d}}{\text{d}x}[ax^{n}+bx^{k}]=c(anx^{n-1}+bkx^{k-1})=acnx^{n-1}+bckx^{k-1}