Pipe diameter: $0\mathrm{.}6m,$ pipe slope: $0\mathrm{.}002,n=0\mathrm{.}015$ ignore infiltration and inflow. Ground elevation at manhole $1$ is $823\mathrm{.}25m$ and the ground elevation at manhole $2$ is $822\mathrm{.}65m.$ The distance between the last two manholes is $120m.$ What is the elevation difference $($in meters$)$ between the invert elevations of these two manholes ANSWER $$S $0\mathrm{.}24$ BE CAREFUL $!!!$