In Exercises $19-22,$ calculate the Riemann sum $R(f, P, C)$ for the given function, partition, and choice of sample points. Also, sketch the graph of $f$ and the rectangles corresponding to $R(f, P, C)$.
$$
f(x)=x^{2}+x, \quad P=\{2,3,4.5,5\}, \quad C=\{2,3.5,5\}
$$