$B$ = $\frac{36}{1.3.5}$ + $\frac{36}{3.5.7}$ + $\frac{36}{5.7.9}$ +...+ $\frac{36}{25.27.29}$
= $9$ .( $\frac{4}{1.3.5}$ + $\frac{4}{3.5.7}$ + $\frac{4}{5.7.9}$ +...+ $\frac{4}{25.27.29}$)
= $9$ .( $\frac{1}{1.3}$ - $\frac{1}{3.5}$ + $\frac{1}{3.5}$ - $\frac{1}{5.7}$ +...+ $\frac{1}{25.27}$ - $\frac{1}{27.29}$ )
= $9$ .( $\frac{1}{1.3}$ - $\frac{1}{27.29}$ )
= $9$ .( $\frac{1}{3}$ - $\frac{1}{783}$ )
= $9$ . $\frac{260}{783}$
= $\frac{260}{87}$