20 men can build 56 m long wall in 6 days. What length of a similar wall can be built by 70 men in 3 days?

Let the required length be L m.
More men, More length (Direct proportion)
Less days, Less length (Direct proportion)
Men 20 : 70
Days 6 : 3
∴ (20 x 6 x L) = (70 x 3 x 56)
∴ L = (70 x 3 x 56) / (20 x 6) = 98 m