\[\begin{array}{l}
a)\frac{3}{9} + \frac{9}{{15}} + \frac{8}{{12}}\\
= \frac{1}{3} + \frac{3}{5} + \frac{2}{3}\\
= \left( {\frac{1}{3} + \frac{2}{3}} \right) + \frac{3}{5}\\
= \frac{3}{3} + \frac{3}{5}\\
= 1 + \frac{3}{5}\\
= \frac{5}{5} + \frac{3}{5}\\
= \frac{8}{5}\\
b)\frac{4}{{10}} + \frac{{12}}{{32}} + \frac{9}{{15}}\\
= \frac{2}{5} + \frac{3}{8} + \frac{3}{5}\\
= \left( {\frac{2}{5} + \frac{3}{5}} \right) + \frac{3}{8}\\
= \frac{5}{5} + \frac{3}{8}\\
= 1 + \frac{3}{8}\\
= \frac{8}{8} + \frac{3}{8}\\
= \frac{{11}}{8}
\end{array}\]

3/9 + 9/15 + 8/12 

= 1/3 + 1/5 + 2/3 

= ( 1/3 + 2/3 ) + 3/5 

= 1 + 3/5 

= 8/5 

b 4/10 + 12/32 + 9/ 15 

= 2/5 + 3/8 + 3/5 

= ( 2/5 + 3/5 ) + 3/8

= 1 + 3/8 

= 11/8

a.3/9+9/15+8/12=

=1/3+3/5+2/3

=(1/3+2/3)+3/5

=1+3/5

=8/5

b.4/10+12/32+9/15

=2/5+3/8+3/5

=(2/5+3/5)+3/8

=1+3/8

=11/8