Answer:
250 m
Step-by-step explanation:
Let the total length be x m.
[tex] \therefore \: \frac{3}{5} \times x = 210 \\ x = 210 \times \frac{5}{3} \\ x = 70 \times 5 \\ x = 350 \: m \\ \\ \frac{5}{7} \times x = \frac{5}{7} \times 350 = 5 \times 50 = 250 \: m[/tex]
