Symmetric Shapes

Remember that if a procedure called, say, shape produces a total turtle turn of 360/n degrees then the command repeat n [shape] will have the symmetry of a regular polygon with n sides.

If we have:
to shape
fd 20 lt 135 fd 20 rt 45 fd 30 rt 30
end

and, if repeat 10[shape rt ?] has the symmetry of a regular decagon, what is the size of the turn?


Note that, when drawing a semicircle, the total turtle turn is 180 degrees:
If repeat 5[semicircle lt ?] produces:
what is the size of the turn?