[tex]\displaystyle a \cdot \frac{2}{3} \cdot \frac{14}{13} = \frac{11}{15} \\ \\ a \cdot \frac{28}{39} = \frac{11}{15} \\ \\ a= \frac{11}{15} : \frac{28}{39} \\ \\ a= \frac{11}{15} \cdot \frac{39}{28} \\ \\ a= \frac{429}{420} ^{(3} \\ \\ a= \frac{143}{140} [/tex]
