[tex] \large \displaystyle{ \qquad \dashrightarrow\frac{3}{7} \times \frac{63}{21} \times \frac{49}{15}}[/tex]

[tex] \large \displaystyle{ \qquad \dashrightarrow\frac{3}{7} \times \frac{7 \times 3 \times 3}{7 \times 3} \times \frac{7 \times 7}{3 \times 5}}[/tex]

[tex] \large \displaystyle{ \qquad \dashrightarrow\frac{ \cancel3}{ \cancel7} \times \frac{7 \times 3 \times \cancel3}{ \cancel7 \times \cancel3} \times \frac{ \cancel7 \times \cancel7}{ \cancel3 \times 5}}[/tex]

[tex] \large \displaystyle{ \qquad \dashrightarrow \frac{7 \times 3}{5}}[/tex]

[tex] \large \displaystyle{ \qquad \dashrightarrow \frac{21}{5}}[/tex]

Answer:

[tex] \frac{3}{7} \times \frac{63}{21} \times \frac{49}{15} \\ = \frac{3}{1} \times \frac{7}{5} \\ = \frac{21}{5} \\ = 4.2.[/tex]