First picture, the one with a a wave above -2pi
Hope this image helps! Sorry if it's hard to read, I had to use the mouse to write it.
The points are:
(-6,6)
(-2,5)
(6,3)
The least common multiple of 4 and 6 is 12.
In similar triangles, the ratios of corresponding sides are equal.
This means
y/6=5/(4+5)
Cross multiply
y=5*6/(4+5)=30/9=10/3 (or 3 1/3)