A sewer has a diameter of 300 mm and slop of 1 in 400. While running full it has a mean velocity of 0.7 m/s. If both the diameter and slope are doubled (to respectively be 600 mm and 1 in 200), what will be the changed mean velocity when running half-full? Use Manning’s formula. (a) 1.59 m/s (b) 2.80 m/s (c) 0.90 m/s (d) 1.00 m/s