$\frac{3030}{1717}\times\frac{343434}{151515}\times\frac{2121}{1818}$
$=\frac{30\times101}{17\times101}\times\frac{34\times10101}{15\times10101}\times\frac{21\times101}{18\times101}$
$=\frac{30}{17}\times\frac{34}{15}\times\frac{21}{18}$
$=\frac{15\times2}{17}\times\frac{17\times2}{15}\times\frac{7\times3}{2\times3\times3}$
$=\frac{2\times7}{3}$
$=\frac{14}{3}$