constants k and m for a function is continuous in entire real number line

Question

Find the constants $k$ and $m$ in the function below such that the function $f(x)$ is continuous in the entire real numberline

$$ f(x)= \begin{cases} 2 & \text{ if }x<_3\\ kx+m & \text{ if }3<x<5\\ 15 & \text{ if }5<x \end{cases} $$