a) ${{21} \over {11}} \times {{22} \over {17}} \times {{68} \over {63}}$

$= \frac{21\times 22\times 68}{11\times 17\times 63}$

$= \frac{21\times 11\times 2 \times 17\times 4}{11\times 17\times 21\times 3}$

$= \frac{2\times 4}{3} = {8 \over 3}$

b) \({5 \over {14}} \times {7 \over {13}} \times {{26} \over {25}} = {5 \over {25}} \times {7 \over {14}} \times {{26} \over {13}} = {1 \over 5} \times {1 \over 2} \times 2 = {1 \over 5}\)