The best answer a good task to start learning lisp its just basic elements like arcs and lines. So have a go only way to learn.
Here is the input part to get you started. Multi getvals is in the download area have a look at the ducting while your there.
(if (not AH:getvalsm)(load "Multi Getvals.lsp"))
(setq ans (AH:getvalsm (list "Enter bend values" "Enter ID" 8 7 "0.5" "Enter OD" 8 7 "0.52" "Enter radius" 8 7 "0.5" "Enter bend Dist" 8 7 ".52" "Enter Bend width" 8 7 "0.05")))
(setq id (atof (nth 0 ans))
od (atof (nth 1 ans))
rad (atof (nth 2 ans))
dist (atof (nth 3 ans))
wid (atof (nth 4 ans))
)