Explanation:
the wrong ratios were compared.
the ratio of corresponding line segments is the same :
RS/RQ = ST/QU
5/6 = 10/x
5x = 60
x = 12
also the second question can be seen as 2 projections with the same angle at different distances of the projection screen.
the baseline has 2 segments : 11 and 29-11 = 18.
the ratio between both segments is the same as the ratio of both legs:
11/18 = 16.5/p
11p = 297
p = 297/11 = 27
and the 3rd question is exactly based on the same structure.
the ratio of the baseline segments is the same as the ratio of the legs, as both sides of the central line are equal projections of different distances at the same projection screen :
4/6 = 8/y
4y = 48
y = 12