Question 830536
a) I assume the floor is perfectly horizontal.
If the legs of of your desk/table are perfectly vertical, the angle measured in part a) would be {{{90^o}}} .
However, The legs of your desk/table may be a little wider apart at the floor than at the top. In that case, I suppose you are expected to measure is the smallest angle.
{{{drawing(300,300,-5,5,-2,8,
line(-5,0,5,0),line(-1,0,1,8),locate(-0.5,1.5,76^o),
arc(-1,0,2,2,-76,0),arc(-1,0,4,4,-180,-76),
locate(-2,2,104^o),locate(2,0,floor),
arrow(3,4,0,4),locate(3.1,4.3,leg)
)}}} That would be the {{{76^o}}} angle.
 
b) and c) You should choose smaller and larger angles, depending on what the legs of your desk are like.
Houses are usually full of {{{90^o}}} angles between the walls and the floor.
If your desk's legs are perfectly vertical, then you will have to look for angles smaller and larger than {{{90^o}}} . 
In my house, the frame around some doors looks like this:
{{{drawing(500,250,-7,7,-6,1,
rectangle(-6,0,6,-7),rectangle(-5,-1,5,-7),
line(-6,0,-5,-1),line(5,-1,6,0),
arc(-6,0,1.8,1.8,0,45),locate(-5.2,0,45^o),
arc(5,-1,1.9,1.9,-45,90),locate(5,-0.7,135^o)
)}}} where the pieces that make the frame have {{{45^o}}} and {{{135^o}}} angles.
Picture frames have those angles too.
The {{{135^o}}} angles should work for part b),
and the {{{45^o}}} angles should work for part c).
Other angles:
In my house there are also slanted ceilings that make {{{135^o}}} angles with the walls.