We just learned that a $K(x,z)=(x)*(z),$ where $(x)$ is a feature mapping. Let $K_1$ and $K_2$ be $R^n{R}^n$ kernels, and $cin{R}^{+}$be a constant. ${}_1$:$R^n{R}^d$ and ${}_2$:$R^n{R}^d$ are feature mappings of $K_1$ and $K_2.$ Let $K_3$ and $K_4$ two new kernels. What are their feature transformations ${}_3$ and ${}_4?$

a$)K_3(x,z)=c{K}_1(x,z)$

b$)K_4(x,z)=K_1(x,z)K_2(x,z)$