reaction engineering $-$ how do you derive both equations? $($from levenspiel's$)$

${}_A{x}_A={}_B{x}_B,\frac{a{}_A}{C_{A0}}=\frac{b{}_B}{C_{B0}}$

$\frac{C_R}{C_{A0}}=\frac{(\frac{r}{a})x_A+\frac{C_{R0}}{C_{A0}}}{1+{}_A{x}_A}$